Technical Report
TR-10-19
Principal organic materials in a
repository for spent nuclear fuel
Lotta Hallbeck, Microbial Analytics Sweden AB
January 2010
Svensk Kärnbränslehantering AB
Swedish Nuclear Fuel
and Waste Management Co
Box 250, SE-101 24 Stockholm Phone +46 8 459 84 00
TR-10-19
ISSN 1404-0344
CM Gruppen AB, Bromma, 2010
Tänd ett lager:
P, R eller TR.
Principal organic materials in a
repository for spent nuclear fuel
Lotta Hallbeck, Microbial Analytics Sweden AB
January 2010
This report concerns a study which was conducted for SKB. The conclusions
and viewpoints presented in the report are those of the author. SKB may draw
modified conclusions, based on additional literature sources and/or expert opinions.
A pdf version of this document can be downloaded from www.skb.se.
Contents
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.11
1.12
1.13
1.14
1.15
1.16
Organic material and microbial degradation processes
Background
Aerobic degradation of organic material
Anaerobic degradation of organic material
1.3.1 Fermentation
1.3.2 Anaerobic respiration
The chemical composition of microorganisms
1.4.1 The amount of organic material in biofilms – the microbial cells
1.4.2 The amount and composition of organic material in biofilms
consisting of cells and exudates
1.4.3 Fungi
1.4.4 Photosynthetic organisms
Biodegradation of organic material produced by microorganisms, fungi, and
photosynthetic organisms
Organic material in the ventilation air
1.6.1 Seeds
1.6.2 Pollen
1.6.3 Spores
1.6.4 Organic dust
Biodegradation of organic material from the ventilation
Organic material in construction material
1.8.1 Concrete
1.8.2 Asphalt
1.8.3 Bentonite clay
1.8.4 Wood
1.8.5 Steel
Degradation of organic material in construction materials
1.9.1 Concrete, grout and shotcrete
1.9.2 Asphalt
1.9.3 Bentonite
1.9.4 Wood
Diesel and emissions from diesel engines
1.10.1 Other particles from vehicles
Degradation of diesel and related emissions
Detergents and lubricants
1.12.1 Detergents
1.12.2 Hydraulic oils and lubricants
Degradation of detergents and lubricants
1.13.1 Detergents
1.13.2 Lubricants
Organic materials from human activities
1.14.1 Tobacco products
1.14.2 Dust from human skin and hair
1.14.3 Fibres from clothes
1.14.4 Urine
1.14.5 Plastics and paper
Degradation of organic material from human activities
1.15.1 Tobacco products
1.15.2 Dust from skin and hair
1.15.3 Fibres from clothes
1.15.4 Urine
1.15.5 Plastics and paper
Organic material from blasting and/or rock-drilling
1.16.1 Blasting
1.16.2 Rock drilling
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3
2
2.1
Inventory and mass estimates of organic material in the repository area
Organic material in buffer and backfill in the repository system
2.1.1 The deposition holes
2.1.2 The deposition tunnels
2.1.3 Plugs in deposition tunnels
2.1.4 The main and transport tunnels
2.1.5 The central area
2.1.6 Ramps and shafts
2.1.7 Top sealing
2.1.8 Total amounts of organic material in buffer and backfill
Organic material in underground constructions
2.2.1 Rock support
2.2.2 Grouting
Foreign and stray organic material left in the repository
2.3.1 Organic materials in stray material left in the repository
Organic material in microbial biofilms
Estimates of the amounts of organic material left in the repository system
2.5.1 Estimates of the total amounts of organic material in buffer, backfill,
rock-support structural elements, and grouting
2.5.2 Estimates of the total amounts of organic material in foreign material
in the repository
2.5.3 Calculations of water volumes in the repository
Evolution with time: degradation processes
2.6.1 Organic material in bentonite
2.6.2 Concrete additives
2.6.3 Degradation of carbohydrates
2.6.4 Degradation of hydrocarbons
2.6.5 Time scale for the degradation of organic materials in the deposition
tunnels in Forsmark and Laxemar
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3
Summary and conclusions
57
4
References
61
2.2
2.3
2.4
2.5
2.6
4
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50
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1
Organic material and microbial
degradation processes
1.1
Background
The interim reports on SKB’s assessment of the long-term safety of a KBS-3 repository /SKB
2004a, b/ describes several issues concerning geochemical aspects of the near field of the repository
that need to be analysed. In the KBS-3V concept, copper canisters with a cast iron insert containing
spent nuclear fuel are surrounded by bentonite clay and deposited at a depth of approximately 500 m
in saturated granitic rock. The chemical evolution of the buffer, backfill, and rock is ultimately
governed by the composition and flow of the groundwater. During excavation and the relatively
long operational period, groundwater will change substantially in composition around the repository.
The effects of several disturbances introduced into the groundwater system due to the activities of
repository construction and operation are relevant. In this regard, it is important to understand the
chemical status of the repository system at closure in order to describe its immediate geochemical
evolution after closure.
One disturbance identified in a spent fuel repository is the presence of organic material. Although it
is known that such material will influence the system, there are no clear indications as to the extent
of the disturbance introduced. Organic materials may be decomposed through microbiologically
mediated reactions, thus adding reducing capacity to the near field of the repository. However, these
materials might also be detrimental by enhancing the potential for radionuclide transport in ground­
water. The possible effects of these materials in the safety assessment (SR-Site) have to be reviewed
from a chemical and microbiological standpoint /SKB 2006/.
Organic compounds can play an important role in transporting radionuclides through the near
and far fields of a radioactive waste repository because of their ability to form mobile complexes,
participate in redox reactions, and sorb onto solid surfaces and thereby make surfaces unavailable to
radionuclides. A good understanding of radionuclide behaviour is dependent on accurate predictions
of radionuclide speciation and therefore must take account of complexes with organic material.
Various categories of organic material may be left in a spent fuel repository after construction
is complete. There will be organic material produced by living organisms in the rock and tunnel
environments, as well as material brought into the repository by constructors. Finally, the mere presence of various human activities will generate organic material that remains in the repository, unless
it is removed or its deposition is prohibited in the first place. The main groups of possible residual
organic materials in repository systems are:
• various types of microorganisms and small plants in the tunnels,
• organic material entering with the ventilation air,
• organic material in construction, buffer, and sealing materials,
• organic material in fuels and from vehicle emissions,
• detergents and lubricants,
• organic material from human activities,
• organic residues from blasting and/or rock-drilling operations.
Construction and stray material made of steel can by its possibility to corrode anaerobically under
production of H2 contribute to microbial growth by H2-utilising microorganisms. One scenario is that
acetogens produce acetate from H2 and CO2. The acetate in combination with H2 can then be used by
sulphate-reducing bacteria that produce H2S by their metabolism.
This report focuses on the following: identifying organic material that may be present in repository
systems at the time of closure (unless removed); the chemical composition, structure, and main organic
degradation products of the identified material; and the microbial processes that will affect this material.
H2S produced from H2 produced from anaerobic corrosion of steel will be addressed. The report ends
with a summary including recommended actions to deal with the different types of organic material.
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5
1.2
Aerobic degradation of organic material
Biodegradation is a redox process by which organic material is oxidised. In complete oxidation, all
organic carbon is converted into carbon dioxide. In aerobic degradation, the organic molecules are
oxidised by oxygen and converted into carbon dioxide and water:
CH2O + O2 → CO2 + H2O
Eq. 1‑1
Polymeric molecules will be split into monomers by the action of exoenzymes produced by micro
organisms. Molecules such as proteins and nucleic acids, which contain nitrogen, sulphur, and
phosphate, are degraded as shown in Figure 1‑1. Some of the nitrogen, sulphur, and phosphate groups
are separated and expelled from the cell. As long as there is degradable organic material available,
most of these nutrients will immediately be assimilated by the degrading microorganism and used in
biosynthesis, and will not be released to the environment. Chemo-autotrophic microorganisms will
use available nutrients in their biosynthesis as well.
1.3
Anaerobic degradation of organic material
There are two types of anaerobic degradation: fermentation and anaerobic respiration. A general
schematic of microbial degradation is shown in Figure 1‑2, which shows the order in which the
different microbial processes occur in an anaerobic environment. All biodegradation starts with
the hydrolysis of polymers to oligo- and monomers. The monomers are then oxidised to other
compounds or optimally to carbon dioxide by the different groups of microorganisms, depending
on the electron acceptors available in the environment.
1.3.1 Fermentation
In anaerobic systems containing great amounts of organic material, fermenting microorganisms
will thrive. Fermentations are degradation pathways that do not require external electron acceptors.
Instead, electrons are shuffled around within the degraded molecule that has been split into two
or more compounds. The degradation products consist of both more reduced and oxidised organic
molecules, such as organic acids, ketones, and alcohols. Fermentation of sugar commonly yields
carbon dioxide and ethanol.
Protein
Peptides
Lipid
Fattyacids + Glycerol
Nucleicacid
Polysaccharide
Aminoacids
CO2+ H2O
Purines
Uric acid+
Pentoses
Pyrimidines
Dihydrouracil +
Pentoses
Sugars
Acetate
TCA
cycle
+
+
NH4 + SO42−+ PO43−
Pyruvate
Figure 1‑1. Aerobic degradation of major cell components. The tricarboxylic acid (TCA) cycle is one of
the key pathways in many degradation systems.
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Hydrolysis
Monomers
Hydrolysis
Organicpolymers
Aerobic bacteria
Denitrifying
bacteria
Oligo - and
monomers
Manganesereducing bacteria
Ironreducingbacteria
Fermenting
bacteria
Acetate
Organicacids,
alcohols
O2 H2O
H2+ CO2
Sulphatereducing bacteria
CO2
NO3 N2
CO2
Mn4+ Mn2+
CO2
Fe3+ Fe2+
CO2
SO42- S2S0
S2-
Sulphurreducing bacteria
CO2
CH4
Methanogens
Syntrophicbacteria
Acetogenic
bacteria
CO2
H2+ CO2
Acetate
Figure 1‑2. Microbial degradation and the involved microbial groups.
Two fermenting bacteria common in the environment and often found in soil are Bacillus and
Clostridium. Both are spore formers, but the Clostridium genus consists of obligate anaerobes,
whereas the Bacillus genus contains obligate aerobes, facultative anaerobes, and fermenting species
/Madigan et al. 2003/. An example of the fermentation pathway of B. licheniformis is as follows
(Eq. 1‑2):
3 glucose → 2 glycerol + 2.3–butanediol + 4 CO2 Eq. 1‑2
From glucose, the fermenting organism produces glycerol, 2.3-butanediol, and carbon dioxide.
Some Clostridium species ferment sugars and occasionally starch and pectin to form butyric acid,
acetic acid, CO2, and H2 as the principal end-products. As the acids in these fermentations accumulate, so-called butyric acid bacteria begin to produce more neutral compounds, including acetone and
butanol, from the acids. There are several other fermentation pathways in other species of fermenting
organisms, but the details of those pathways is beyond the scope of this report /Madigan et al. 2003/.
1.3.2 Anaerobic respiration
In natural environments, anaerobic respiratory organisms follow a certain progression (see Figure 1‑2).
The first anaerobic respiration metabolisms that are activated when oxygen is depleted are those
connected with the nitrate-, iron-, and manganese-reducing bacteria. These organisms degrade shortchain organic acids such as lactic acid and acetic acid but rarely larger organic molecules such as
six-carbon sugars. The next metabolic type is represented by the sulphate-reducing bacteria, which
use the sulphur in sulphate as an electron acceptor and produce hydrogen sulphide. The carbon and
energy sources for sulphate reducers are short-chain organic acids.
In a system containing large amounts of organic material, such as compost, various fermentation processes should theoretically produce considerable hydrogen that could be used by methanogens and/or
acetogens. In a deep groundwater system, on the other hand, the amounts of hydrogen produced from
the degradation of organic material from the surface or, as in the case discussed here, residual organic
material in the repository is probably quite small. Therefore, the last part of the degradation chain
depicted in Figure 2-2 would be insignificant. This process, based on hydrogen from the degradation
of organic materials, must be distinguished from the methanogenesis and acetate production that
frequently occur in deep groundwater, using hydrogen coming from thermo-catalytic processes in
very deep environments inside the Earth /Pedersen 2001/.
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1.4
The chemical composition of microorganisms
Though it can vary somewhat, the chemical composition of most bacterial cells is fairly similar. An
average bacterial cell has a total weight of 9.5 × 10−13 g and a dry weight of 2.8 × 10−13 g /Niedhardt
et al. 1990/. Table 1-1 lists the weights of the different macromolecules in an average Escherichia
coli cell.
Various types of microorganisms will grow on the tunnel surfaces of a repository during the construction and operational phases. Microorganisms growing on surfaces produce a film consisting of cells
and a gel matrix, called a biofilm. The matrix comprises extracellular material, often polysaccharides
/Christensen and Characklis 1990/. Most of the biological growth in a repository environment will
occur in various types of biofilms, wherever there is liquid water.
1.4.1 The amount of organic material in biofilms – the microbial cells
The number of microorganisms present in a biofilm depends on the environment, i.e. the nutrients
available, water flow, oxygen concentration, surface structure, and temperature. Differences in
these variables will be reflected in both the number of bacteria per unit of surface area and the
biofilm thickness. To estimate the amount of organic material contained in cells in a biofilm, various
reported cell densities are evaluated here. The first such biofilm density, reported by /Pedersen and
Ekendahl 1990/, was measured on glass slides placed in water flowing from a depth of 680 m in
borehole KLX01 in Laxemar, in Småland, south east Sweden. This biofilm contained approximately
109 microorganisms per m2 and can be regarded as a low-density biofilm compared to the other evaluated biofilm density, reported by /Pedersen et al. 1986/, that was established using a pure culture
of Pseudomonas sp. The biofilm contained 1012 microorganisms per m2 and is here referred to as a
high-density biofilm. In both studies, the glass slides were incubated for a short time, i.e. for days or
weeks, and only one layer of microorganisms developed. In older biofilms, several layers of microorganisms can develop. Table 1‑2 presents calculations of the number of microorganisms per m2, the
corresponding biofilm thickness, and the amount of organic material contained in microorganisms in
hypothetical biofilms. These calculations indicate that the cell contribution to the amount of organic
material in a biofilm can range from 10 μg m−2 to 3.0 g m−2. The contribution of microorganisms in
biofilms growing on tunnel surfaces is more likely to be in the range of 0.1–1,000 mg m−2 of organic
material, because the low organic material content of the inflowing groundwater. On special spots
with residual organic material a biofilm could growth to higher density.
1.4.2
The amount and composition of organic material in biofilms consisting
of cells and exudates
Organotrophic biofilms
Organotrophic microorganisms, the group that degrades organic carbon by a respiratory metabolism,
often produce an amorphous, extracellular matrix lacking microscopically recognisable structures.
This matrix usually almost exclusively comprises extracellular polysaccharides (EPSs). This gel-like
material is formed when organic macromolecules are partly hydrated and partly cross-linked
/Christensen and Characklis 1990/. The monomer building blocks of bacterial EPSs can be the
following monosaccharides, uronic acids, and amino sugars: rhamnose, fucose, arabinose, xylose,
mannose, glucose, glucuronic acid, galacturonic acid, mannuronic acid, N-acetylglucosamine, and
2-keto-3-deoxy-octulosonic acid (KDO). Some bacteria produce EPSs consisting of homopolysaccharides. For example, several Acetobacter species produce extracellular cellulose that is chemically
similar to cellulose in higher plants, i.e. β-1,4-linked unbranched glucans.
Thickness and density vary among biofilms. Heterotrophic, EPS-producing biofilms from different
environments were reported to have thicknesses ranging from 10 to 1,300 μm /Christensen and
Characklis 1990/. The density of these biofilms was 5–105 kg m−3. Calculations of the amount
of organic material per m2 in biofilms are presented in Table 1‑3. Three different densities were
arbitrarily chosen, i.e. 10, 25, and 75 kg m−3. These calculations indicate that the amount of organic
material in a biofilm can vary between 0.1 and 75 g m−2 depending on biofilm thickness and density.
Based on the calculations of organic material in the biofilm microorganisms, between 0.1 and 1% of
the organic material in a biofilm consist of microorganisms; the remainder consists of EPSs.
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Table 1‑1. Overall macromolecule composition of an average E. coli cell /Niedhardt et al. 1990/.
Cell constituent
Weight per cell (10−15 g)
Protein
155
RNA
59
DNA
9
Lipid
26
Lipopolysaccharide
10
Murein
7
Glycogen
7
Total macromolecules
Soluble pool
273
8
Total dry weight
284
Total weight
950
Table 1‑2. Amount of organic material contained in the microorganisms of a biofilm, together
with cell density and number of cell layers.
Cell density per layer (m−2)
Number of cell layers
Organic material (g m−2)
Low density:
3.5 × 109
1
1 × 10−5
3.5 × 109
10
1 × 10−4
3.5 × 109
100
1 × 10−6
High density:
1 × 1012
1
0.03
1 × 1012
10
0.3
1 × 1012
100
3
Table 1‑3. Amount of organic material in a biofilm depending on biofilm thickness and density.
Biofilm thickness
(mm)
Estimated biofilm density
(kg m−3)
Amount of organic material
(g m−2)
0.01
10
0.1
0.1
10
1
1
10
10
0.01
25
0.25
0.1
25
2.5
1
25
25
0.01
75
0.75
0.1
75
7.5
1
75
75
Biofilms of iron- and manganese-oxidising bacteria
The most striking biofilm growth on tunnel walls and in ditches is that produced by the iron- and
manganese-oxidising bacteria. Several species in this group of bacteria produce extracellular material that has a distinct and recognisable shape.
Among the iron oxidisers, the species Gallionella ferruginea and Leptothrix ochracea are predominant.
Both were discovered by microscopy and described in the literature /Ehrenberg 1836, Kützing 1843/ in
the first half of the nineteenth century.
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Gallionella ferruginea
In the Äspö Hard Rock Laboratory (HRL) tunnel, the main biofilm-forming bacterium is the iron
oxidiser Gallionella ferruginea. This bacterium produces large quantities of organic material, in the
form of a helical stalk, and oxidises iron on the tunnel walls and floor at all positions in the tunnel
where reduced ferrous-iron-containing groundwater intrudes and flows. /Anderson and Pedersen
2003/ measured the biofilm formation of Gallionella and its influence on iron oxide precipitation and
the partitioning of lanthanides and actinides. Most of this study was done using a bacteriogenic iron
oxide reactor, in situ, continuous flow (BRIC) apparatus. The sampled material was produced inside
growth tubes in the BRIC and simulated a biofilm growing in the tunnel very well. In this study,
the Gallionella organisms produced stalks up to approximately 50 μm long from each cell. The cell
density ranged from 105 to 106 per mL in the growth tubes. The BRIC system contained bacteria other
than G. ferruginea, but the cell counting method used did not distinguish between different species.
The results of in situ BRIC experiments in the Äspö HRL showed a good correspondence with those
from in vitro laboratory experiments in which G. ferruginea was grown in pure cultures. In the growth
tubes, the highest measured number of Gallionella cells was 2.5 × 106 per mL, the average stalk
length was 34 μm per cell, and the maximum stalk length was 60 μm /Hallbeck and Pedersen 1990/.
/Hallbeck and Pedersen 1995/ reported that a Gallionella biofilm grown in groundwater used for
heat-exchange purposes had a total organic carbon (TOC) content of 0.147 μmol cm−2 and a Fe
content of 0.330 μmol cm−2. This study also demonstrated that the carbon/nitrogen ratio (C/N) of cells
was 4.3 and of cells and stalk material was 6.8. The C/N ratio of E. coli cells is reported to be 3.4
/Niedhardt et al. 1990/. If the C/N ratio of cells in an iron-oxidising biofilm is assumed to be 4, based
on the above data, the ratio between carbon in cells and in biofilms will be 1.7, i.e. there will be 1.7
times more carbon in Gallionella biofilms than in the same cells not forming a biofilm. Iron-oxidising
biofilms will consequently have a carbon content of 85% content compared to biofilms without stalks,
for example, a carbon conten of 50% for the E. coli cells presented in Table 1‑1. Calculations of the
organic material content of biofilms cannot, therefore, be based on cell numbers only.
Using the TOC numbers for biofilm formation presented in /Hallbeck and Pedersen 1995/,
0.147 μmol carbon cm−2 corresponds to 17.6 mg carbon per m2, which in turn corresponds to
20.8 mg of organic material per m2 if we assume that 85% of the OM is carbon.
The biofilm on the glass slides described above was estimated to be 30 μm thick and represented a
thin biofilm of iron oxidisers. If extrapolated, this would represent 690 g per m3 of organic material.
Biofilms up to 10–15 cm thick can be formed on tunnel walls, which corresponds to approximately
70–100 g organic carbon per m2 of overgrown tunnel wall assuming equal densities of the biofilms
– a significant amount of organic material that should be accounted for. In reality, the water content
decreases as the biofilm thickness increases, suggesting that the carbon content can be higher.
Composition of the stalks and sheaths of iron and manganese oxidisers
The chemical composition of Gallionella stalks is still unknown. Published titration studies of
Gallionella cells and stalks /Martinez et al. 2003/ demonstrated that functional groups with acidic,
basic, and neutral pKa values were present. Some of these groups are important for the sorption of
iron oxides and consequently radionuclides to surfaces. /Emerson and Ghiorse 1993a, b/ analysed
the composition of the sheaths of the sheath-forming and manganese-oxidising bacterium Leptothrix
discophora, finding that dry sheaths consisted of 38% C, 6.9% N, 6% H, and 2.1% S. The sheath
mass was distributed into the following groups of compounds: 34–35% carbohydrates (polysaccharides), 23–25% proteins, 8% lipids, and 4% inorganic ash. The recovery of the analyses was
approximately 70% of the total mass. The polysaccharides consisted of a 1:1 mixture of uronic acids
e.g. glucuronic acid, galacturonic acid, and mannuronic acid and at least one unidentified uronic
acid) and one amino sugar, galactosamine. Nine per cent of the dry weight was 2–3 deoxyoctanoic
acid. The surface of the sheaths probably contains several hydroxyl groups possessing binding
properties for cations.
Biofilms of sulphur-oxidising bacteria
At some places in the Äspö HRL, sulphur-oxidising bacteria can be found, including both unicellular
and filamentous organisms. The filamentous group is represented by species of Thiothrix, a sheath-
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forming bacterium that stores elemental sulphur inside its cells. This bacterium oxidises hydrogen
sulphide with oxygen. It is thought to use organic carbon as a source of carbon and reduced electrons.
Many other sulphur-oxidising bacteria are autotrophic and use carbon dioxide as a carbon source
/Madigan et al. 2003/.
The composition of the sheaths of Thiothrix and other filamentous sulphur oxidisers is not well
explored. One reference suggests that the extracellular material is composed of cellulose because
of its neutral sugar composition, the results of methylation analysis, and the identification of free
oligosaccharides /Ogawa and Maki 2003/.
The literature on biofilms of sulphur-oxidising bacteria is also sparse. A sulphur-oxidising biofilm
probably contains about the same amount of organic material as does a biofilm of iron oxidisers.
This suggestion is based on the observation that sulphur-oxidising bacteria commonly occur
intermixed with iron oxidisers in the Äspö HRL.
1.4.3 Fungi
Fungi belong to the Eukaryotes, which are organisms possessing a true nucleus and other cellular
organelles. The cell wall of fungi consists mostly of chitin, although cellulose is present in some
/Madigan et al. 2003/. Chitin is a polymer of the glucose derivative N-acetylglucosamine (Figure 1‑3).
It is laid down in micro-fibrillar bundles, just as is cellulose. Fungal cell walls are generally composed
of 80–90% polysaccharides, with protein, lipids, polyphosphates, and inorganic ions making up the
wall-cementing matrix. In some fungi, other glucans such as mannans, galactosans, and chitosans
replace chitin in the fungal cell wall. Fungi often spread via spores, which are very resistant to heat
and desiccation.
Moulds
Moulds are filamentous, non-differentiated, multi-cellular fungi that are widely distributed in nature.
Moulds grow with hyphae that produce asexual spores called conidia, which give moulds their dusty
appearance. Filamentous fungi are responsible for the decomposition of wood, paper, and cloth,
for example. Both cellulose and lignin are decomposed by fungi, and lignin is decomposed almost
exclusively by wood-rotting fungi. Lignin-decomposing fungi are called “white rot” and cellulosedecomposing fungi are called “brown rot”, since they leave the lignin unchanged. White rot fungi
also decompose cellulose /Madigan et al. 2003/.
Yeasts
Yeasts are unicellular fungi. The best-studied yeast is Saccharomyces cerevisiae, also called baker’s
yeast or brewer’s yeast. /Ekendahl et al. 2003/ reported the existence of yeasts in deep granitic
groundwater. It is therefore plausible that yeasts might grow in biofilms on rock surfaces in a
repository. The yeasts isolated from Äspö HRL groundwater were closely affiliated with Rhodotorula
minuta and Cryptococcus sp. Many yeast species can live both with and without oxygen, and in
anoxic systems use a fermentative metabolism; for example, S. cerevisiae produce ethanol anaerobically /Madigan et al. 2003/.
OH
C H2
OO H
OH
HO
NH
H 3C
O
Figure 1‑3. N-acetylglucosamine molecule.
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1.4.4 Photosynthetic organisms
During the repository construction and waste deposition phases, there will be electric light sources
along the tunnels in the repository. In most places where the light intensity is high enough and water
is present, light-harvesting photosynthetic organisms such as cyanobacteria, green algae and small
plants like mosses will grow. This is seen in most tunnels and mines and in the Äspö HRL tunnel and
ONKALO in Finland, cyanobacteria are common where the illumination is strong. Mats of mosses
are growing on the tunnel floor at some locations, for example, between 1,320 and 1,335 m along the
Äspö tunnel.
Cyanobacteria
The cyanobacteria belong to the domain Bacteria and are thus organisms without cell nuclei. Many
species live as unicellular entities, but filamentous and colony-forming types of cyanobacteria are also
common. Some cyanobacteria have cell walls containing peptidoglycan, like those of Gram-negative
bacteria. Others have cell walls consisting of cellulose /Nobles et al. 2001/. Many cyanobacteria
produce extracellular material resembling envelopes or sheaths that bind groups of cells or filaments
together in jelly-like masses.
Since cyanobacteria are photosynthetic, they contain photosynthetic pigments such as chlorophyll a
and phycobilins. These pigments are found in large amounts in membrane structures inside the cells
/Madigan et al. 2003/.
Many cyanobacteria have nitrogen-fixing ability. In some species, this unique process takes place
in specialised cells called heterocysts, the cell walls of which contain large amounts of glycolipids.
In nitrogen-fixing cyanobacteria, up to 10% of the cell mass can consist of a nitrogen copolymer of
aspartic acid and arginine called cyanophycin.
The chemical composition of the biomass of two cyanobacteria, Phormidium sp. and Spirulina
maxima, indicates that the proportions of the main cell components differ considerably (Table 1‑4).
Extracellular polymeric substances of cyanobacteria
The extracellular polymeric substances produced by cyanobacteria vary between species. The sugar
components of the extracellular polymeric substance of a pure culture of Phormidium 94a were
galactose, mannose, galacturonic acid, arabinose, and ribose /Vicente-Garcia et al. 2004/. Another
study of four filamentous cyanobacteria and one coccoid, single-celled green algae demonstrated that
the extracellular polymeric substance contained 7.5–50.3% protein and 16.2–40.5% carbohydrates
/Hu et al. 2003/; these carbohydrates included monosaccharides such as mannose, glucose, galactose,
arabinose, and rhamnose.
Unicellular green algae
Green algae should not be confused with cyanobacteria, since they belong to a completely different
domain of organisms. Green algae are eukaryotic organisms and thus have a cell nucleus and other
cell organelles. In green algae, photosynthesis takes place in organelles called chloroplasts. The
cell walls of green algae consist of cellulose and their main carbon reserve materials are starch and
sucrose /Perry et al. 2002, Madigan et al. 2003/. The cells themselves contain all the components
included in bacterial cells (see Table 3‑1).
Unicellular green algae are often found in environments inhabited by cyanobacteria, and are
therefore likely found in green biofilms supported by artificial light sources in a repository.
Table 1‑4. The percentage chemical composition of Phormidium sp. and Spirulina maxima
biomasses grown on synthetic media (% dry weight) /Cañizares-Villanueva et al. 1995/.
Component
Phormidium sp
Spirulina maxima
Protein
53.4
45.5
Lipids
Carbohydrates
Ash
12
9.4
2.5
27.5
42.5
9.7
9.5
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Mosses
Mosses are plants without clear differentiation between stems and leaves. They have a cell nucleus
and other cell organelles, such as chloroplasts and mitochondria. Their cell walls are composed of
cellulose and their carbon reserve material is starch.
Mosses thrive in environments with relatively low light intensity and high humidity. They are not a
common part of the biota in tunnels and caves, but have been observed in the Äspö HRL tunnel as
mentioned above.
1.5
Biodegradation of organic material produced by
microorganisms, fungi, and photosynthetic organisms
The organic material produced by microorganisms will be degraded by other microorganisms during
both the construction and deposition periods. During the construction period, most of the degradation
will be aerobic, when oxygen is present. The first part of the deposition period in the closed repository
will still be aerobic, but within a relatively brief time the oxygen will be consumed by the degradation
of organic material and anaerobic processes will become ascendant.
Since the organic material discussed above is produced by living organisms, most of it is in turn
degradable by microorganisms, given enough time, if water is available. This conclusion is based on
the prominent role of microorganisms in perpetuating life and can be summed up in two principles
referred to as Van Niel’s postulate /Perry et al. 2002, p. 238/.
• There are microorganisms present in the biosphere that can utilise every constituent part or
product of living cells as sources of carbon and/or energy.
• Microbes with this capacity are present in every environmental niche on Earth.
Even if the degradation processes of one organism do not run all the way to carbon dioxide,
the organic waste products of this organism will be further degraded by other microorganisms.
Fermentation products are good examples of such waste products. Acids, alcohols, and ketones
produced during fermentation can act as complexing agents, but will probably be consumed by other
microorganisms present in groundwater in the repository long before any radionuclides can possibly
escape a canister.
1.6
Organic material in the ventilation air
The air coming from the ground surface via the ventilation system to the repository tunnels will
contain organic material, comprising seeds, pollen grains, spores, and dust.
1.6.1 Seeds
Seeds from plants carry all the nutrients necessary for the development of the new plant until a
functional root and the first leaves have grown. The chemical composition of seeds therefore differs
from that of the vegetative cells of plants.
Seeds from cane berries, Rubus spp. such as red raspberry, blackberry, and cloudberry, contain
6–7% protein and 11–18% oil /Bushman et al. 2004/. It is difficult to find the chemical composition
of coniferous seeds therefore some other examples are given. The composition varies mostly with
the amount of lipids. Most data are found on lipid rich seeds. The seeds of Xylopia aethiopica, a
rainforest tree, contain 63.65 g of carbohydrates, 12.45 g of protein, and 9.58 g of lipids per 100 g of
seed (wet weight) /Barminas et al. 1999/. Another example is dry weight composition of date seeds
which contain 5.5% protein, 10–13% of oil and 81–83% carbohydrates /Besbes et al. 2004/. The
carbohydrate in seeds is starch, which hydrolyses to sugar in a germinating seed. The composition
of the seeds is of minor importance for the safety assessment..
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13
1.6.2 Pollen
Pollen grains contain the male gametophyte produced by angiosperms and gymnosperms. They are
the vegetative and generative cells formed after meiosis (i.e. reduction division) of the microspore
structure. They are usually between 10 and 100 μm in diameter and are encapsulated in a complex,
sculptured cell wall.
Pollen grains contain cellulose and polymers consisting of carotenoids and carotenoid esters. They
also contain lipids as an energy source, phytates as a phosphorous source, as well as enzymes, and
RNA and DNA /Rowley et al. 1981, Brooks and Shaw 1968/.
1.6.3 Spores
Spores can be both the asexual reproduction bodies of filamentous fungi and the reproduction structures of cryptogams. These spores resemble seeds and pollen grains in their structure and composition.
1.6.4 Organic dust
This kind of dust comes from living organisms and consists of a wide array of different biomolecules.
1.7
Biodegradation of organic material from the ventilation
The seeds, pollen grains, and spores borne by the ventilation air into the repository are products
of living organisms and are generally biodegradable. The seeds and spores can germinate in the
repository, as in the case of the moss in the Äspö HRL tunnel. Plant material, if not removed, will
be degraded by microorganisms when the tunnels are closed and backfilled. One special property
of seeds and spores is that the outer part is very resistant. If they do not germinate or are not biodegraded, nothing else will affect them and they will probably remain intact, buried in the repository.
Organic dust can also be degraded by microorganisms.
The amounts of seeds, pollen grains, spores, and dust vary over the course of the year with peaks in
spring, summer, and early autumn.
1.8
Organic material in construction material
1.8.1 Concrete
Concrete is a cement paste containing various filling materials, all of which are inorganic. To
enhance various properties of concrete, several additives can be added to the paste. The degradation
of these additives will, given time, generate low-molecular-weight organic materials and eventually
carbon dioxide. These additives can be divided into accelerating, retarding, water reducing, superplasticising, and air-entraining agents /Lindvall 2001/.
Accelerators are inorganic salts, the most commonly being CaCl2. There are also alternative accelerators such as 2,2-imino-diethanol, which is biodegradable, at least in aerobic environments.
Retarders are any reactive chemicals that extend the pumping time and/or thickening time of cement
slurry; among the more common are powdered, organic retarders, such as lignosulphonates (solid)
or organosulphonates (liquid). These compounds are adsorbed to or precipitated on the surface of
the cement particles. Cellulose derivatives such as carboxymethyl hydroxyethyl cellulose (CMHEC)
have also been used as cement retarders for many years.
Antifoamers or defoamers are added to concrete to reduce foaming during mixing operations. These
are usually organophosphates.
Water-reducing additives reduce the water content of the cement paste by up to 15%, and the
most commonly used ones are lignosulphonates and sulphonated naphthalene or formaldehyde
(Figure 1‑4). These additives disperse the cement particles because of their dipolar charging properties, and comprise 0–0.1% of concrete by weight.
14
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CH2
SO3 Na
n
Figure 1‑4. Chemical structure of naphthalene sulphonate.
Superplasticisers are the same as the water-reducing additives but have stronger effects. They are
used to lower the mix water requirement of concrete and are added in amounts up to 0.4% by wet
weight. Superplasticisers can be broadly classified into four groups:
1. sulphonated melamine-formaldehyde condensates (SMFs),
2. sulphonated naphthalene-formaldehyde condensates (SNFs),
3. modified lignosulphonates (MLSs),
4. others, including sulphonic acid esters and carbohydrate esters.
Most available data, however, pertain to SMF- and SNF-based admixtures, which are supplied as
either solids or aqueous solutions. One of the most common superplasticisers is sodium-sulphonated
naphthalene formaldehyde condensate (Na-SNFC). Other known superplasticisers are polymers of
sulphonated melamine formaldehyde, sodium lignosulphate, and gluconic acid /Gascoyne 2002/.
Air-entraining agents (AEA) are used to enhance the resistance to freeze-thaw action by increasing
the air content of the concrete. The most commonly used such compounds are acryl sulphonates,
alkyl sulphonates, and phenol ethoxylates, which are added in amounts up to 0.01% by wet weight.
1.8.2 Asphalt
Asphalt is composed of a bituminous binding agent and a stone material. The binding agent can be in
the form of bitumen, soft bitumen, or bitumen emulsion. Bitumen, which has thermoplastic properties, is a distillation product of crude oil. Road oil and bitumen lacquer are other products used in
asphalt, along with bitumen emulsion which is bitumen and water mixed together with an emulsifier
/Swedish National Encyclopedia 1990a, b/.
The composition of bitumen is greatly dependent on the source of the crude oil and the distillation
procedure, but the main fraction comprises various heavy hydrocarbons. Bitumen is what is often
left after refining has yielded gasoline, diesel, and other fuels. This fraction includes very heavy
organic molecules that often contain oxygen, sulphur, and nitrogen atoms in their structures /Tissot
and Welte 1984/. The chemical composition and physical properties of bitumen are still not fully
understood.
1.8.3 Bentonite clay
Bentonite is an inorganic clay currently mined in many places around the world. Its chemical name is
hydrated sodium calcium aluminium silicate, and its composition (in wt%) is 9.98% Al, 20.78% Si,
4.10% H, and 65.12% O. The exact composition depends on the origin of the clay.
Chemical analysis data on the organic material in bentonite are very sparse. /Sjöblom 1998/ assumed
that bentonite would become contaminated by organic material in the environment in which it was
deposited and by the operations involved in mining and transporting it. This organic material was
suggested to be humus and the calculated amounts were <0.1 g/kg bentonite from the environment
and <0.1 g/kg bentonite from mining operations. There would also be some contamination with
lubricants, amounting to 0.5 g/kg bentonite, during the compaction of bentonite into blocks.
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15
Humus is a collective name for organic material in soil and water composed of large organic molecules that are not easily degraded. It has three different fractions, one insoluble fraction, humin, and
two soluble fractions, the humic and fulvic acids. Humic acids, which are melanin-like polymeric
aromatic phenols and carboxylic acids, can be isolated by lowering the pH. At pH 2, the humic acids
start to coagulate and the formed precipitate can be separated by filtration, while the fulvic acids are
left in the filtrate. Fulvic acids are small aromatic and aliphatic compounds soluble at all pH values.
They have molecular weights between 1,000 and 10,000 and have many carboxyl and hydroxyl
groups that make them chemically active /Stevenson 1994/.
It has been suggested that three different types of bentonite clays be investigated for potential use in
the repository: Friedland Na+, Milos Ca2+, and Wyoming Na+ bentonites /SKB 2004a/. Analyses of
the organic carbon content of the Milos and Wyoming bentonites are presented in Table 1‑5, where
the weight percentage values are recalculated as the mass of organic material. The gross formula
used for organic material is CH2O.
1.8.4 Wood
The main components of wood are cellulose and lignin /Fries 1973/. Cellulose is a linear polymer of
D-glucose with beta 1,4-linkages (Figure 1‑5), whereas lignin is a polymer with aromatic structures
(Figure 1‑6).
Wood contains secondary compounds produced by the tree; for example, a characteristic compound
produced by the pine tree is pinene, a terpenoid. Tannin is another compound produced by trees and
an example of its structure is shown in Figure 1‑7 /Hagerman and Butler 1994/.
1.8.5 Steel
Although steel is not organic, the anaerobic corrosion of steel could contribute indirectly to the pool
of organic material in a repository. The hydrogen produced in the oxidation–reduction process then
acts as an energy source for various microbial processes.
The details of the process of anaerobic corrosion of steel are still under discussion, but most of the
reactions involved are well known /Cord-Ruwisch 2000/. The main principle of the corrosion process is that protons from the dissociation of water act as electron acceptors in the oxidation of the iron
atoms, resulting in hydrogen formation, see Eq. 1‑3.
Fe0 + 2H+ → Fe2+ + H2
Eq. 1‑3
The hydrogen can be used by sulphate-reducing bacteria, which reduce sulphate to hydrogen sulphide
by oxidising hydrogen, either by autotrophy, with carbon dioxide fixation, or by heterotrophy, using
organic carbon as a carbon source. The produced hydrogen sulphide reacts with the ferrous iron to
form iron sulphide, and by that releases more protons. A schematic of the chemical route is shown in
Figure 1‑8. The energy-transforming reaction in sulphate-reducing bacteria can be written as:
4H2 + SO42− + 2H+→ H2S + 4H2O
Eq. 1‑4
The incorporation of carbon into the cells of sulphate reducers can occur by the addition of carbon
dioxide and hydrogen to acetate. The reaction is described in Eq. 1‑5.
CH3COO−- CoA + CO2 + H2 → CH3COCOO− + CoA + H2O
Eq. 1‑5
The acetate can be produced by the oxidation of hydrogen and the reduction of carbon dioxide made
by acetogens, as described in Eq. 1‑6.
2CO2 + 4H2 → CH3COO− + 2 H2O + H+ Eq. 1‑6
Table 1‑5. Amount of organic material in different bentonite clays.
Bentonite material
Organic carbon
(wt%)
Organic material
(wt%)
Organic material
(kg/ton of bentonite)
Milos Ca2+
0.24
0.64
6.4
Wyoming Na+
0.20
0.5
5.0
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HO CH
2
HO
HO
OH
O
O HO
OH
C H2
OH
Non-reducing end
O
O HO
OH
C H2
O
OH
OH
n-2
Reducing end
Figure 1‑5. The cellulose subunits.
Figure 1‑6. Part of the lignin molecule.
Figure 1‑7. Example of a tannin.
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17
SO42−
H2S
2
Fe2+
FeS
SRB
2H+
3
4
H2
1
2e-
Anode
Cathode
Figure 1‑8. Role of hydrogen-consuming SRB in the anaerobic corrosion of steel. In principle, four different
ways to stimulate the corrosion process can be visualised: 1) consumption of cathodic hydrogen (cathodic
depolarisation), 2) anodic depolarisation by Fe2+ removal, 3) stimulation by formation of an iron sulphide
layer, which may be cathodic, and 4) supply of protons to the cathode.
Acetate production has been reported to occur in Fennoscandian Shield groundwater from the Äspö
HRL /Hallbeck and Pedersen 2008/.
In line with the above theory, rock supports and other steel bolts left in the repository may corrode
and produce hydrogen, which is a possible energy source for some microorganisms, such as sulphate
reducers and acetogens. This will result in the production of hydrogen sulphide and biomass.
1.9
Degradation of organic material in construction materials
1.9.1 Concrete, grout and shotcrete
After hardening, superplasticisers are strongly bound and immobilised within the hydrated phases of
the Portland cement /Onofrei et al. 1992/, although relatively little is known of their precipitation in
insoluble form /Atkins and Glasser 1992/. It is possible that superplasticisers could decompose in a
repository if subjected to radiation /Gascoyne 2002/.
The additives in cement based construction materials are strongly bound to the cement particles. As
long as the structures remain intact, these compounds will remain in place. Removing the structures
will give rise to concrete dust, however, and this will increase the risk of additive release to the
groundwater. Naphthalene sulphonates have been demonstrated to be degraded in aerobic environments /Brilon et al. 1981, Ruckstuhl et al. 2002/.
One problem with the use of organic additives in concrete, grout and shotcrete is that non-polymerised
monomer and oligomer additives can dissolve in groundwater and be flushed away from the fracture
or borehole where they were supposed to remain. This will increase the amount of material that needs
to be used in construction and rock support.
Microbial growth on leakage from grouting has been observed in the Posiva Onkalo tunnel in
Olkiluoto /Pedersen et al. 2008/. The leakage of superplasticisers has also be reported during tunnel
construction in Switzerland /Ruckstuhl et al. 2002/.
1.9.2 Asphalt
Most components of asphalt are large organic molecules with low water solubility. The most soluble
organic molecules are those of the “BTEX” group – benzene, toluene, ethyl-benzene, and xylene –
all of which are biodegradable at slow but significant rates. None of these compounds is found in
large quantities in asphalt.
1.9.3 Bentonite
The organic material in bentonite is assumed to mainly comprise humic substances. These compounds
will probably be bound to clay particles and trapped in the bentonite. A possible problem is the
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oxidation of organic material in the bentonite by sulphate-reducing bacteria to form carbon dioxide
and hydrogen sulphide /Masurat et al. 2010a, b/. If a lubricant will be used during the production of
the bentonite blocks this can be available for degradation.
Humic and fulvic acids contain many carboxylic and hydroxyl groups, which make them possible
complexing agents. In conclusion, the lack of data on organic material in bentonite calls for more
thorough investigation of the amounts and composition of this organic material.
1.9.4 Wood
The cellulose part of wood is readily degraded by both bacteria and fungi. These organisms produce
extracellular cellulolytic enzymes, which break the bonds in cellulose to form glucose units /Perry
et al. 2002/. Furthermore, cellulose easily degrades under alkaline conditions, commonly occurring
in nuclear repositories built of cement. The main degrading reactions of cellulose as well as the main
degradation products are described in section 1.15.5.
Lignin, on the other hand, is only degraded by the white rot fungi (basidiomycetes). The degradation
involves the action of oxygen, peroxides, and the enzyme ligninase. Though fungi do not use lignin
in their metabolism, other microorganisms can use the phenolic degradation products as substrate
/Perry et al. 2002/.
Secondary compounds produced by trees, for example, pine tree tannins, are slowly biodegradable.
Their chemical structure with many hydroxyl groups makes them potential complexing agents. For
example, sawdust was traditionally used to reduce clogging by iron precipitates in drainage systems
because of the ability of tannins to bind iron.
Most wood constructions will probably be removed before repository closure. A source of wood
material that might be more problematic to eliminate is sawdust from construction work that has
ended up in drainage water or become mixed with gravel.
1.10 Diesel and emissions from diesel engines
Diesel is a distillation product of crude oil defined by the temperature interval used in distilling it,
i.e. 150–350°C. Given this temperature range, diesel is a very complex mixture of compounds with
different properties. The largest part of diesel is alkanes, but diesel also contains polyaromatic hydrocarbons (PAHs), alkyl-benzenes, branched or unsaturated aliphatic hydrocarbons, and sulphur. The
exact composition of diesel varies from type to type; the diesel in Sweden with the best environmental
specifications is called MK‑1 diesel (see Table 1‑6; /Swedish National Road Administration 2002/).
The products of complete combustion are carbon dioxide and water. Combustion in diesel engines,
however, is generally incomplete. Unless efficient filters and catalysts are installed, there will be particles in emissions from diesel engines. These particles are 0.1–0.3 μm in size; they mostly comprise
soot (carbon) from the engine, but also contain water, sulphuric acid, and condensed hydrocarbons.
Diesel that is partly or completely made from organic material, such as waste products from the
sugar and/or forest industries, is also available. These diesel products may emit less of the condensed
hydrocarbons and sulphuric acids that are found in diesel produced from mineral oil.
Table 1‑6. Composition of MK‑1 diesel.
Compound
MK‑1 diesel
Polyaromatic hydrocarbons (PAHs)
Maximum 200 ppm, often below 80 ppm
Aromatic hydrocarbons
Maximum 5 wt%
Benzene
Not detectible
Olefins
Not detectible
Sulphur
Maximum 10 ppm, often 1–5 ppm
Oxygenates
Not added
Cyclo-aliphates, naphtenes
Not regulated up to 50 wt%
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19
1.10.1 Other particles from vehicles
Tyre wear can also produce particulate matter consisting mostly of rubber, some of which contains
PAHs. The chemical name of natural rubber is isoprene. The rubber in tyres is cross-linked with
sulphide bridges to enhance the elastomeric properties /Swedish National Encyclopedia 1992b/
Particles from brake linings can be deposited on the rock walls and floor. These particles are mostly
metal, mainly copper, and do not contain organic material /Johansson et al. 2004/.
1.11 Degradation of diesel and related emissions
If a diesel spill occurs in a repository during construction, most of the diesel will be pumped out
with the infiltrating groundwater. Some of the diesel may adhere to the surfaces of rock material, but
it will probably be biodegraded in the presence of oxygen and water. Hydrocarbons have very low
solubility in water, and there will be a two-phase system if diesel and water come into contact. Since
it is an equilibrium system, there will be a slow partitioning of hydrocarbons into water for a long
time. The components of diesel are different kinds of hydrocarbons, most of which are degraded by
bacteria in both aerobic and anaerobic environments. In anaerobic environments, diesel hydrocarbons are degraded by sulphate- and/or iron-reducing bacteria /Meckenstock et al. 2000, Annweiler
et al. 2002, Eriksson et al. 2005/.
Condensed polyaromatic hydrocarbons, PAHs, are large molecules that are more slowly degraded,
especially in anaerobic systems, than are aromatic or aliphatic hydrocarbons, although the anaerobic
degradation of PAHs has been reported /Annweiler et al. 2002/.
The organic material from diesel will probably have a negligible influence on the safety assessment,
except as a source of oxygen-consuming carbon compounds in microbial degradation. Diesel
remaining after the oxygen is consumed will be degraded by anaerobic microorganisms. Aerobic
degradation of natural rubber (NR) in tyres has been reported /Tsuchii and Tokiwa 2006/. When NR
is mixed with synthetic isoprene rubber only the NR is degraded. Rubber particles will in the repository will probably generally not be degraded by microorganisms. The oxygen will be consumed by
more readily degraded OM and the flow of water will decrease considerably when the buffer and
backfill is fully saturated.
1.12 Detergents and lubricants
During repository construction, detergents and lubricants will be used at many places.
1.12.1 Detergents
Surfactants are the most widely used ingredients in detergents and degreasing agents. The two most
common surfactant groups are linear alkylbenzene sulphonates (LASs) and alkylphenol ethoxylates
(APEs) (see Figure 1‑9 (a) and (b), respectively). LASs are the quantitatively most important
surfactants for household and industry. Surfactants based on plants are also available.
1.12.2 Hydraulic oils and lubricants
As discussed in section 2.3, the main sources of hydrocarbons in the repository are diesel oil and
hydraulic and lubricating oils. Oil spills usually contain a complex mixture of aliphatic hydrocarbons, PAHs, and cyclic hydrocarbons.
Lubricants are widely used in all kinds of vehicles and machines. There are both natural, i.e. mineral
and plant based, and synthetic lubricants, the main components of which are fats and oils. Various
additives can be added to lubricants.
20
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CH3 ( CH2 )n CH ( CH2 )n'CH3
(a)
SO3
C9H19
O [ CH2CH2O ] n CH2CH2 OH
(b)
Figure 1‑9. Molecular formula of generic (a) LASs and (b) APEs.
Dispersants keep sludge, carbon, and other deposit precursors suspended in oil; detergents keep the
engine parts clean of deposits; and rust/corrosion inhibitors prevent or control oil oxidation, varnish
and sludge formation, corrosion, and viscosity increase. Extreme-pressure (EP), anti-wear, and friction
modifiers form protective films on engine parts and reduce wear and tear. Metal deactivators form
surface films so that metal surfaces do not catalyze oil oxidation. Pour-point depressants lower the
freezing point of oils, assuring free flow at lower temperatures, while antifoamers reduce foam in the
crankcase and during blending /Leugner 2005/.
Lubricating oils have a broad profile in the C18–C40 range, with resolved alkanes being almost
entirely absent. Common types of lubricating oils include crankcase oil, transmission fluid, hydraulic
fluid, and cutting oil. In some hydraulic fluids, the PAH concentrations can be much lower than in most
other refined products. However, as stated by /Wong and Wang 2001/, degrading lubricant oils can also
be an important source of PAHs.
1.13 Degradation of detergents and lubricants
1.13.1 Detergents
The natural degradation of LASs appears to be very efficient under oxic conditions, reaching levels
of 95–99% and with half-times of between a few to hundreds of days. The breakdown of LAS
surfactants involves the degradation of the straight alkyl chain, the sulphonate group, and finally
the aromatic group /Scott and Jones 2000/. Half-life time reported in the same review was from 1 to
117 days depending on surfactant, environment and temperature.
On the other hand, APEs are less biodegradable than LASs. Estimated biodegradation ratios are
between 0–20% /Swisher 1987, Scott and Jones 2000/. In addition, restrictions on the use of APEs
have arisen since the discovery that their breakdown products are more toxic to aquatic organisms
than are the APEs themselves.
The biodegradation of APEs leads to the shortening of the ethoxylate chains to form alkylphenol
carboxylates, leading ultimately to the formation of nonyl- and octylphenols. Nonylphenol (NP) is
approximately 10 times more toxic to water living organisms than its ethoxylate precursor and also
more persistent to degradation.
Many of the tensides and emulsifiers used formerly had long and heavily branched non-polar chains.
Those products are poorly biodegradable and some, for example, alkylphenol ethoxylates, have
degradation products that are very stable /Swedish National Encyclopedia 1995/.
Several emulsifiers and tensides made from plant sources or produced by microorganisms are
now available on the market. These products are biodegradable and do not produce long-lived
metabolites.
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21
1.13.2 Lubricants
Lubricants can also be mineral or plant based. Plant-based fats and oils are more easily degraded,
wheras mineral oils degrade slowly.
Degradation is fastest in oxygenated environments, and tensides, emulsifiers, and lubricants will
form part of the pool of organic material that contributes to oxygen consumption in the repository
after closure.
Of all the organic compounds found in oils or refined petroleum products, the monoaromatic hydrocarbons are the most water soluble /Eganhouse et al. 1996/. Consequently, benzene and its alkylated
derivatives are the hydrocarbons most frequently found in groundwater. Once groundwater moves
away from the oil source, microbial degradation is the dominant process controlling the fate of these
compounds /Eganhouse et al. 1996, Massias et al. 2003/.
It should be noted that no single strain of bacteria has the metabolic capacity to degrade all the
components of crude oil. In nature, the biodegradation of crude oil typically involves a succession
of species in the consortia of microbes present /Venosa and Zhu 2003/. Petroleum degradation
involves progressive or sequential reactions in which certain organisms carry out the initial attack
on a petroleum constituent; this produces intermediate compounds subsequently used by a different
group of organisms in a sequential process that results in further degradation.
The characterisation of bacterial communities that grow efficiently in the presence of hydrocarbons
has been the subject of decades of academic and industrial research /Zobell 1946, Atlas 1977, Foght
et al. 1990, Pelletier et al. 2004/. Results have been applied in developing commercial fertilizers,
which all involve the addition of nutrients to oily residues and the induction of optimal conditions
for hydrocarbon degrading bacteria (HDB). HDB have been found to be active in most marine environments including the Arctic Ocean. Generally, saturated n-alkanes are the most readily degradable
components of a petroleum mixture /Zobell 1946, Atlas 1981/. The biodegradation of n-alkanes with
molecular weights up to C44 has been demonstrated.
As previously stated, aerobic conditions are generally considered necessary for the extensive degradation of oil hydrocarbons in the environment, since the major degradative pathways of both saturates
and aromatics involve oxygenases /Atlas 1981, Cerniglia 1992/. Many studies have demonstrated that
oxygen depletion leads to sharply reduced biodegradation activity in marine sediments and in soils
/Atlas 1981, Hambrick et al. 1980/.
Although some studies have demonstrated that anaerobic oil degradation occurs only at negligible
rates /Atlas 1981/, recent studies have found that anaerobic hydrocarbon metabolism may be an
important process under certain conditions /Head and Swannell 1999/. The biodegradation of some
aromatic hydrocarbons, such as BTEX compounds, has been clearly demonstrated to occur under
a variety of anaerobic conditions. Studies have also demonstrated that in some marine sediments,
PAHs and alkanes can be degraded under sulphate-reducing conditions at rates similar to those
under aerobic conditions /Caldwell et al. 1998, Coates et al. 1997/. The importance of the anaerobic
biodegradation of oil in the environment still merits further study.
One way to minimise oil spill problems over a longer time scale is to use biodegradable hydraulic oil
and lubrication greases. Most of these oils are based on biological oils and alcohols from mineral oils.
The use of biodegradable hydraulic oils and lubrication greases is an option for the SKB repository
/SKB 2004b/, since, in nature, true biological oils based on rapeseed oil degrade within a few weeks,
synthetic oils within a few months, and mineral oils within several years under aerobic conditions.
1.14 Organic materials from human activities
1.14.1 Tobacco products
Smoking will be prohibited in the repository during both the construction and deposition phases.
Smoking residues will therefore not be present in the repository. However, snuff is widely used in
Sweden and will certainly be used by personnel during the construction and deposition periods,
22
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especially if smoking is prohibited. Instructions should be given how to handle such tobacco when it
is used. Still, a significant amount of the snuff used will certainly be dropped, leaving behind residues.
Snuff is made of dried and ground tobacco leaves to which water and sodium chloride are added.
Propylene glycol is added to maintain the humidity level in the snuff, and sodium carbonate is used
as a pH regulator. Most snuff residues consist of ground tobacco leaves mixed with user saliva. One
portion of snuff weighs approximately 1 g. Nicotine, the predominant alkaloid component of the
tobacco plant, is a tertiary amine composed of a pyridine and a pyrrolidine ring. Nicotine exists in
two different three-dimensional forms or stereoisomers. Tobacco contains only (S)-nicotine (also
called L-nicotine), which is the most pharmacologically active form /Pool et al. 1985/. The nicotine
content of snuff is 8–10 mg per portion; when it has been used, only 10–20% of the nicotine is left,
that is, between 0.8 and 2 mg. Although the major alkaloid in tobacco is nicotine, there are others as
well, including nornicotine, anabasine, myosmine, nicotyrine, and anatabine. These comprise 8–12%
of the total alkaloid content of tobacco products /Piade and Hoffmann 1980/. In some varieties of
tobacco, nornicotine concentrations exceed those of nicotine /Schmeltz and Hoffmann 1977/.
Tobacco mostly consists of plant cell wall material, which consists of pectic acid and small amounts
of galactan and arabane. The cell wall also consists of the polymerisation products of hexoses (i.e.
glucose, galactose, and mannose), of uronic acids (i.e. glucuronic acid and galacturonic acid), and of
some pentoses. Some parts of the leaf are made of cellulose /Fries 1973/.
1.14.2 Dust from human skin and hair
The dust that comes from the human skin consists mainly of dead cells from the outermost cell layer of
the skin and is composed of keratin, a threadlike protein compound /Swedish National Encyclopedia
1992c/. Hair is a special development of the keratin layer of the skin, differing from skin in the higher
sulphur content of its keratin /Swedish National Encyclopedia 1992a/. Consequently, dust from humans
mostly consists of protein compounds.
1.14.3 Fibres from clothes
The fabrics used in working clothes are made of synthetic fibres and/or cotton. Polyester is the mostused synthetic fibre. Refined and bleached cotton fibre comprises up to 99% cellulose (see cellulose
in section 1.15.5).
1.14.4 Urine
Construction personnel must be informed of the importance of keeping the tunnel clean of waste of
different kinds. Portable toilets will be available at convenient intervals in the tunnel during construction, but some urination will probably take place in out-of-the-way locations. The main organic
components of urine are urea, creatinine, ammonia, uric acid, amino acids, and other inorganic
components such as sodium, chloride, sulphate, and carbonate /Lehninger 1982/.
1.14.5 Plastics and paper
Plastics are synthetic materials made from fractions of natural gas or crude oil changed chemically
into solid form. These fractions are the building blocks of plastics and they form chemically linked
subunits called monomers; long chains of monomers in turn form polymers that compose plastics.
There are two basic types of plastic, thermosetting and thermoplastics. Thermosetting plastics are
moulded into a permanent shape and thereafter cannot be softened. These plastics are used primarily
for multiple-use items, such as dishes and furniture. Thermoplastics become soft when exposed to
heat and pressure and harden when cooled. Thermoplastics are the most common type of plastic and
are used to make a variety of products.
Paper is made of cellulose. Cellulose is a relatively common material in low- and intermediate-level
radioactive repositories, due to its presence in daily use objects such as tissues, clothes, and paper.
However, its presence poses an important risk to repository assessment, due to the complex binding
capacity of polyhydroxy ligands, which is described in section 1.8.4.
TR-10-19
23
1.15 Degradation of organic material from human activities
1.15.1 Tobacco products
The tobacco residues from snuff mainly comprise plant leaf material and will be easily degraded by
microorganisms, thus contributing to oxygen consumption in a closed repository.
The destruction of nicotine by microorganisms was investigated by /Batham 1927/, who observed
an increase in the nitrate content of soil to which nicotine had been added. He assumed that this
increase was due to the conversion of the alkaloid to nitrate by soil bacteria. The quantitative
destruction of nicotine in a synthetic medium by individual species of bacteria was studied by
/Bucherer and Enders 1942/ (cited in /Hylin 1958/), who isolated three organisms in pure culture.
/Wada and Yamasaki 1953/ reported the destruction of nicotine by a microbe as well, while /Tabuchi
1954/ further characterised and classified this microorganism. In addition, /Hylin 1958/ described
several organisms isolated in pure culture from tobacco seeds and from soil. Nicotine-decomposing
bacteria described by several investigators /Sguros 1954, Conn and Dimmick 1947, Weber 1935,
Wenusch 1942, 1943, Bucherer 1942, 1943, Hylin 1958, Frankenburg and Vaitekunas 1955, Wada
and Yamasaki 1953, 1954/ have been reported to be both aerobic and anaerobic depending on the
microbial species.
The ability to use nicotine as a carbon and nitrogen source seems to be possessed by relatively few
microorganisms, since the toxicity of this substrate inhibits the adaptation of many bacteria to using
it as a metabolite.
Some degradation products have been identified as products of microbial nicotine degradation,
including 6-hydroxynicotine and 6-hydroxy-3-succionoylpyridine /Hylin 1958, Frankenburg
and Vaitekunas 1955/. In addition, nicotine oxidation may produce 3-carboxylic pyridine acid or
nicotinic acid.
1.15.2 Dust from skin and hair
The proteins in skin and hair will be degraded by microorganisms in the repository, including both
aerobic and anaerobic bacteria.
1.15.3 Fibres from clothes
Cellulose fibres will be degraded by microorganisms, including both bacteria and fungi. Polyesters,
on the other hand, are relatively resistant to biodegradation. The possible amounts of fibres from
clothes are expected to be minor and will most likely be washed out with drainage water from
cleaning of the tunnels before closure.
1.15.4 Urine
Urine contamination in the repository positively affects the biodegradation of most organic material,
as it constitutes an additional nitrogen source. Nitrogen is generally a limiting nutrient when energy
and carbon are available in excess.
The great amount of biodegradable substrate in urine triggers rapid microbial growth, which strongly
alters its chemical composition. One dominant reaction is the decomposition or hydrolysis of urea, a
microbially catalyzed reaction that produces ammonia and raises the pH above 9.
Urea is the major component of urine. The release of urea to an environment is known to affect
the N cycle. Urea hydrolyses rapidly, producing ammonia and releasing OH−, Urea hydrolysis is
catalysed by the large heteropolymeric enzyme urease using a bimetallic nickel centre. Urease
occurs in a wide range of organisms, and the organisms able to degrade urea using this enzyme
include bacteria, algae, fungi, and higher plants. The primary function of this enzyme is to let the
organism use urea as a nitrogen source. Urease, like any enzyme, is a catalyst that increases the
chemical reaction rate without being affected itself.
During urea hydrolysis, an unstable intermediate product forms that rapidly degrades to ammonia
and carbon dioxide. This intermediate product is H2NCOONH4 (ammonium carbamate) although,
24
TR-10-19
due to its instability, the transformation of urea in soil can essentially be described by the following
overall reaction:
H2N-CO-NH2 + 3 H2O → 2 NH4+ + OH− + HCO3−
Eq. 1‑7
During hydrolysis, soil pH can increase to pH > 7 because the reaction requires H+ from the soil
system.
1.15.5 Plastics and paper
In recent years, several of biodegradable thermoplastics have been developed. A plastic is known
as biodegradable when living organisms (e.g. fungi, bacteria, and algae) can attack the chemical
structure of the polymer to convert it into nutrients. The susceptibility of a plastic to biodegradation
depends on its chemical structure, and polyethylene or polyester are just slightly biodegradable,
whereas polyurethanes are very biodegradable. A biocompatible polymer is one that does not
damage any living organism, either by chemical effects or because of its own biodegradability.
For example, poly tetramethylene succinate, an aliphatic polyester with a high-melting-point, was
found to be degradable by some soil bacteria in an aerobic environment /Pranamuda et al. 1995/. In
addition, polyurethane, polyester polyurethanes, and polyether polyurethanes were reported to be
degraded by microorganisms, especially fungi, in an aerobic environment /Nakajima-Kambe et al.
1999/. The repository environment will become oxygen-depleted relatively quickly after closure, and
there are limited supplies of the important nutrients nitrogen and phosphorous, so plastic degradation
will probably be very slow. Unless removed in advance, plastics will therefore remain in the repository for a considerable time.
Paper left in the repository will be degraded by microorganisms according to the degradation of cellulose (see section 1.9.4). Cellulose easily degrades under alkaline conditions without the presence
of microorganisms. This is a common process assumed to occur in nuclear repositories containing
concrete as part of the engineering barriers. There will be some concrete left in repository but the
main backfill material will be bentonite and rock so the alkaline degradation of cellulose is not likely
to happen to any greater extent. The process will however be described here.
There are three main degrading reactions: i) the peeling-off reaction, ii) the base-catalysed cleavage
of glycosidic bonds (alkaline hydrolysis), and iii) the formation of nonreactive end groups through
the chemical transformation of reducing end groups to metasaccharinate, which in fact are interrelated /Van Loon and Glaus 1998, Glaus and Van Loon 2004/. Isosaccharinic acid (ISA) is the
main product of anaerobic cellulose degradation formed at room temperature /Van Loon and Glaus
1998/. ISA is a general term for 3-deoxy-2-C-(hydroxymethyl)-D-aldonic acids with both α and β
diastereoisomers. Its structural formula is shown in Figure 1‑10.
Furthermore, ISA has been conclusively identified as a key component of the degradation products
of cellulose, being one of the organic materials most responsible for influencing the speciation and
mobility of radionuclides in a radioactive waste repository.
HO
O
C
HOH2C
C
OH
H
C
H
H
C
OH
C H2OH
Figure 1‑10. α-Isosaccharinic acid.
TR-10-19
25
In general, carbon mass balances indicate that the large majority of reaction products found in
solution can be explained by the formation of ISA and other low-molecular-weight carboxylic
acids. On the other hand, as described elsewhere /Motellier and Charles 1998, Glaus et al. 1999/,
some other degradation products of cellulose can be identified at alkaline pH. These degradation
products include glycolic acid, lactic acid, acetic acid, formic acid, and metasaccharinate, although
together they represent only 10% of the total dissolved organic compounds. All of them are acids
with important complexation capacity. Table 1‑7 presents the degradation kinetics of cellulose for a
final analysis time of 239 days.
1.16 Organic material from blasting and/or rock-drilling
Depending on the method used for construction, i.e. either blasting or rock drilling, the activity will
leave a certain amount of debris.
1.16.1 Blasting
Paper and plastic material from cables and detonators are typical blasting residues (see section 1.14.5).
In mining considerable amounts of unused explosives might be left. During the construction and
before closure of the repository, cleaning procedures will minimise the risk for this and is not included
in the calculations of the amounts of foreign materials that will be left in the repository /Lindgren
et al. 2009 a, b/.
A Canadian study demonstrated that blasting left nitrate on rock surfaces and in the groundwater
/Stroes-Gascoyne and Gascoyne 1998/. Although nitrate is not an organic material, it can affect
organic material since it is a crucial nutrient for microorganisms. A supply of extra nitrate will
increase the possibility of degradation of the organic material left in a repository. Nitrate is also
an electron acceptor for nitrate-reducing microorganisms and will be consumed quickly when the
repository starts to become anaerobic (see section 1.3.2).
1.16.2 Rock drilling
Rock drilling machines may leave spills of various hydrocarbons, as discussed above (see section 1.10).
Table 1‑7. Degradation kinetics of cellulose. Product concentrations are relative to the total DOC
content in %. Data from /Glaus et al. 1999/.
Analytes
7 days
40 days
62 days
119 days
181 days
239 days
Formic
0.60
1.22
1.09
1.19
1.30
1.30
Acetic
1.80
2.66
2.12
2.39
1.93
2.07
Glycolic
0.37
0.71
0.66
0.70
0.83
0.85
Pyruvic
0.20
0.23
0.17
0.11
0.13
0.10
Glyceric
0.46
1.68
1.27
0.90
1.05
0.94
Lactic
1.22
1.79
1.51
1.60
1.63
1.59
Threonic
1.59
1.77
1.32
0.94
0.99
1.16
Isosaccharinic
56.6
85.0
76.1
74.0
78.1
77.1
DOC (mM)
123
317
471
685
784
910
26
TR-10-19
2
Inventory and mass estimates of organic material
in the repository area
2.1
Organic material in buffer and backfill in the
repository system
As described previously, organic materials will remain in both buffer and backfill. This section
compiles estimates of the amount of organic material left in different parts of the repository system
at closure. The categorisation follows that used in the report SKB TR-06-21 and is as follows:
•
•
•
•
•
deposition holes,
deposition tunnels,
transport tunnels,
central area,
shafts and ramps.
In the final summary, the repository area is divided into the deposition area, comprising deposition holes
and tunnels, and other areas, comprising the remaining tunnels, central area, shafts, and ramps. The estimates of the amount of organic material are based on the dimensions of the different parts as described
in Layout D2 for Forsmark with 6,000 canisters and Layout D2 for Laxemar, also with 6,000 canisters.
Table 2‑1 presents the dimensions of Forsmark and Table 2‑2 the dimensions of Laxemar.
Table 2‑1. Dimensions used for estimating the amount of organic material remaining in the
Forsmark repository according to Layout D2 from /Lindgren et al. 2009a/.
Area
Theoretical area (m2)
Total length (m)
Deposition holes
Theoretical volume (m3)
Rock volume* (m3)
1.15 × 105
1.15 × 105
1.2 × 106 a)
Deposition tunnels
19 (23)*
52,200
1.0 × 10
Main and transport
tunnels
60 (69)*
6 a)
10,700
5.57 × 10
5 b)
6.40 × 105 b)
Central area
2,900
1.19 × 105 c)
1.36 × 105 c)
Shafts and ramps
Shafts: 800
Ramps: 4,700
2.16 × 10
5 d)
2.45 × 105 d)
Total
71,300
2.007 × 106
2.336 × 106
* the extra blasting volume is included
a)
including chamfering of the deposition holes
b)
including chamfering of deposition tunnels and roofs
c)
including rock-loading station
d)
including exhaust air shaft in the deposition area.
Table 2‑2. Dimensions used for estimating the amount of organic material remaining in the
Laxemar repository according to Layout D2 from /Lindgren et al. 2009b/.
Area
Theoretical area (m2)
Total length (m)
Deposition holes
Theoretical volume (m3) Rock volume* (m3)
1.15 × 105
1.15 × 105
Deposition tunnels
19 (23)*
80,400
1.54 × 10
1.8 × 106 a)
Main and transport
tunnels
60 (69)*
39 (45)*
14,800
7.7 × 10
8.9 × 105 b)
Central area
2,900
1.19 × 105 c)
1.36 × 105 c)
Shafts and ramps
Shafts: 800
Ramps: 5,200
2.36 × 105 d)
2.66 × 105 d)
Total
104,100
2.780 × 106
3.207 × 106
6 a)
5 b)
* the extra blasting volume is included
a)
including chamfering of the deposition holes
b)
including chamfering of deposition tunnels and roof
c)
including rock-loading station
d)
including exhaust air shaft in the deposition area.
TR-10-19
27
2.1.1
The deposition holes
Material in the deposition holes
The volume around the canisters in the deposition holes will be filled with bentonite blocks and
pellets. Figure 2‑1 shows the reference geometry of the copper canister with the surrounding
deposited buffer.
The volume of all deposition holes taken together is calculated to be 1.15 × 105 m3 (see Table 2‑1).
The volume of one copper canister is 4.35 m3, so the volume of 6,000 canisters is 2.61 × 104 m3; the
volume to be filled with bentonite is then 8.89 × 104 m3. If the mean dry density of the bentonite is
conservatively set to 1,780 kg/m3 (see Table 2‑3), there will be a total of 1.58 × 108 kg of bentonite in
the deposition holes, which corresponds to approximately 26 tons of bentonite clay per deposition hole.
Organic material in the deposition holes
The average amount of organic carbon contained in the bentonite used for the repository is reported
to be 0.25 wt%, with an upper limit of 0.40 wt% and a lower limit of 0.1 wt% /Karnland et al. 2006/.
Using these values, the total amount of organic carbon in the bentonite used in deposition holes will
be 3.9 × 105 kg (3.9 × 102 tons), representing 9.8 × 102 tons of organic material. The organic material
in bentonite clay is assumed to be mostly humic and fulvic acids.
1630 mm
Pellets
50 mm
280 mm
1070 mm
6835 mm
785 mm
810 mm
500 mm
Figure 2‑1. Reference geometry of the deposited buffer /SKB 2010a/.
28
TR-10-19
Figure 2‑2. Outline of the reference design for the closure of the main and transport tunnels and the
central area. From /SKB 2010b/.
Table 2‑3. Dry densities of the different types of bentonite structures used in a deposition hole in
a repository. Data from Buffer Production Report.
Bentonite type
Dry density (kg m–3)
Solid blocks
1,705
Ring-shaped blocks
1,770
Pellets
1,820
2.1.2 The deposition tunnels
The reference backfill material in the deposition tunnels will be low-grade bentonite with a 50–60%
content of montmorillonite /SKB 2010a/.
There will be one slit at the top of each deposition hole (see Figure 2‑1). Bentonite pellets will be
poured into the deposition holes through these slits; the total amount of pellets is calculated to be
four tons per deposition hole, representing a total of 2.4 × 104 tons for all 6,000 holes.
Material in the deposition tunnels – Forsmark
The total volume of the deposition tunnels in Forsmark, including the extra blasting rock volume, is
estimated to be 1.2 × 106 m3.
Since the dry densities of both bentonite blocks and pellets are the same, i.e. 1,700 kg/m3, the total
mass of bentonite in the deposition tunnels will be 2.0 × 109 kg or 2.0 × 106 tons.
TR-10-19
29
Table 2‑4. Dry densities of the different types of bentonite structures used in the deposition
tunnels in a repository. Data from /SKB 2010a/.
Bentonite type
Dry density (kg m–3)
Amount of the total volume
60%
Solid blocks
1,700
Pellets
1,700
Bottom bed pellets
1,700
Organic material in bentonite in the deposition tunnels – Forsmark
The average organic carbon content of the low-grade bentonite is 0.25 wt%. The total amount of
organic carbon in the backfill of the deposition tunnels is therefore 5 × 106 kg or 5 × 103 tons, calculated to represent 1.2 × 104 tons of organic material. No exact description is available of the character
of the organic material present in the bentonite clay but it is suggested to be humic and fulvic acids.
Material in the deposition tunnels – Laxemar
The total volume of the deposition tunnels in Laxemar, including the extra blasting rock volume, is
estimated to be 1.8 × 106 m3.
Since the dry densities of both bentonite blocks and pellets are the same, i.e. 1,700 kg/m3 the total
mass of bentonite will be 3.1 × 109 kg or 3.1 × 106 tons.
Organic material in bentonite in the deposition tunnels – Laxemar
The average organic carbon content of the low-grade bentonite is 0.25 wt%. The total amount of
organic carbon in the backfill of the deposition tunnels is therefore 7.5 × 106 kg or 7.5 × 103 tons,
calculated to represent 1.9 × 104 tons of organic material. No exact description is available of the
character of the organic material present in the bentonite clay but it is suggested to be humic and
fulvic acids.
2.1.3 Plugs in deposition tunnels
The plugs in the deposition tunnels consist of several parts that will contribute in different ways to
maintaining plug functions during the different phases of the respository lifetime. The parts of the
reference plug are illustrated in Figure 2‑3.
Materials in the deposition tunnel plugs
The reference plug consists of a concrete plug, a watertight seal made of bentonite blocks and pellets, a filter made of sand or gravel, concrete beams made of reinforced concrete, and drainage pipes
and grouting pipes made of steel and possibly isolated with geotextile. Table 2‑5 summarises the
amounts of these materials in one plug. Transformable components are such that are considered to be
dissolved or transformed in a long-time perspective (Backfill report). Glenium 51 is a polycarboxylic
ether hyperplasticer used in concrete to increase the plasticity of the material.
According to the repository designs, there will be 200 deposition tunnels in Forsmark and 300 in
Laxemar. Table 2‑6 presents the calculated amounts of organic material and steel in the plugs in
both sites.
Organic material in the deposition tunnel plugs – Forsmark
The active and organic component of Glenium 51 is polycarboxylate ether, which comprises 35%
of the product. The total amount of Glenium 51 used in Forsmark is 140 tons, so the amount of the
active component is 49 tons.
Organic material in the deposition tunnel plugs – Laxemar
The total amount of Glenium 51 in Laxemar is 210 tons, which gives 74 tons of the active component.
30
TR-10-19
Grouting pipes
Concrete beams
Backfill end sone
Drainage
Concrete plug
Watertight seal
Filter
Figure 2‑3. Schematic cross-section of the reference design of the plug. Figure from the Backfill
Production Report /SKB 2010a/.
Table 2‑5. Components and substances in the plug and the amounts regarded as stable and
unstable. The amounts have been estimated for one plug.
Part of the plug
Substance
Stable [tons]
Concrete plug
Portland cement
12
Silica fume, densified
8
Water
17
Limestone filler, L25
37
Sand, 0–8 mm
104
Gravel, 8–16 mm
56
Superplasticiser: Glenium 51
(BASF)
Concrete beams
Portland cement
0.6
2.7
Silica fume, densified
1.8
Water
3.7
Limestone filler, L25
8.3
Sand, 0–8 mm
23.3
Gravel, 8–16 mm
12.6
Superplasticiser: Glenium 51
(BASF)
0.1
Reinforcement steel
Filter
Transformable [tons]
6.8
Gravel, 8–16 mm
25.3
Total:
281.2
38
Table 2‑6. The amount of organic material and steel in plugs in Forsmark and Laxemar.
Part of the plug
Substance
Forsmark, 200 plugs (tons)
Laxemar, 300 plugs (tons)
Concrete plug
Superplasticiser:
Glenium 51 (BASF)
120
180
Concrete beams
Superplasticiser:
Glenium 51 (BASF)
20
30
TR-10-19
31
2.1.4 The main and transport tunnels
According to the Closure Production Report /SKB 2010b/, the final design of the backfill for the
main and transport tunnels has not yet been definitely determined, but the same reference design as
for the deposition tunnels, using low-grade bentonite, is proposed.
Material in the main and transport tunnels – Forsmark
The total volume, including extra blasting rock, of the main and transport tunnels in Forsmark is
6.45 × 105 m3 and the dry density of the blocks and pellets of bentonite used totals 1,700 kg/m–3.
The total amount of bentonite in the main and transport tunnels will thus be 1.1 × 109 kg or
1.1 × 106 tons.
Organic material in bentonite in the main and transport tunnels – Forsmark
The average organic carbon content of the low-grade bentonite is 0.25 wt%. The calculated total
amount of organic carbon in the backfill of the main and transport tunnels is 2.8 × 106 kg or
2.8 × 103 tons, calculated to represent 7.0 × 103 tons of organic material. No description is available of the character of the organic material present in the bentonite clay.
Material in the main and transport tunnels – Laxemar
The total volume, including extra blasting rock, of the main and transport tunnels in Laxemar is
8.9 × 105 m3 and the dry density of the blocks and pellets of bentonite used is 1,700 kg/m–3. The total
amount of bentonite in the main and transport tunnels will thus be 1.5 × 109 kg or 1.5 × 106 tons.
Organic material in bentonite in the main and transport tunnels – Laxemar
The average organic carbon content of the low-grade bentonite is 0.25 wt%. The calculated total amount
of organic carbon in the backfill of the main and transport tunnels is 3.8 × 106 kg or 3.8 × 103 tons,
calculated to represent 9.5 × 103 tons of organic material. No description is available of the character of
the organic material present in the bentonite clay.
2.1.5 The central area
The central area will be filled with crushed rock without the addition of any material containing
organic substances.
2.1.6 Ramps and shafts
The ramps and shafts will be filled with a bentonite mixture to a depth of 200 m. The composition is
supposed to be the same as in the deposition tunnels and the bentonite density is 1,700 kg/m3.
Material in the ramps and shafts – Forsmark
The total volume, including extra blasting rock, of the ramps and shafts in Forsmark is 2.45 × 105 m3
and the volume that is to be filled with bentonite is 1.4 × 105 m3. Assuming bentonite of the same dry
density as that used in the deposition, main, and transport tunnels, 1,700 kg/m–3, the total amount of
bentonite used in the ramps and shafts will be 2.4 × 108 kg or 2.4 × 105 tons.
Organic material in bentonite in the ramps and shafts – Forsmark
The average organic carbon content of the low-grade bentonite is 0.25 wt%. The calculated total amount
of organic carbon in the backfill of the main and transport tunnels is 6.0 × 105 kg or 6.0 × 102 tons,
calculated to represent 1.5 × 103 tons of organic material. No description is available of the character of
the organic material present in the bentonite clay.
Material in the ramps and shafts – Laxemar
The total volume, including extra blasting rock, of the ramps and shafts in Laxemar is 2.66 × 105 m3
and the volume that is to be filled with bentonite is 1.6 × 105 m3. Assuming bentonite of the same dry
32
TR-10-19
density as that used in the deposition, main, and transport tunnels, 1,700 kg/m–3, the total amount of
bentonite used in the ramps and shafts will be 2.7 × 108 kg or 2.7 × 105 tons.
Organic material in bentonite in the ramps and shafts – Laxemar
The average organic carbon content of the low-grade bentonite is 0.25 wt%. The calculated total amount
of organic carbon in the backfill of the main and transport tunnels is 6.8 × 105 kg or 6.8 × 102 tons,
calculated to represent 1.7 × 103 tons of organic material. No description is available of the character of
the organic material present in the bentonite clay.
2.1.7 Top sealing
The top sealing is assumed to extend to a depth of 200 m and will be backfilled with blast rock and
moraine as described in the Closure Production Report /SKB 2010b/. From 200 to 50 m beneath
the ground surface, the volume will be filled with crushed rock with a maximum particle size of
200 mm, with a size distribution of the Fuller type. The uppermost 50 m of the ramps and shafts
will be backfilled with very coarse crushed rock that must be effectively compacted to minimise selfcompaction. Above this level, masonries of well-fitted rock blocks forming a “jigsaw puzzle” will be
constructed. Silica concrete will be poured into the joints for mechanical sealing (description from
the Closure Production Report /SKB 2010b/).
2.1.8 Total amounts of organic material in buffer and backfill
Table 2‑7 and Table 2‑8 summarise the amounts of organic material in the buffer and backfill in
Forsmark and Laxemar, respectively; also included is the amount of organic material in concrete
used in the deposition tunnels.
Table 2‑7. Amount of bentonite and organic material in the Forsmark repository according to
Layout D2.
Area
Theoretical volume
(m3)
Bentonite dry density
(kg m–3)
Amount of bentonite
(kg/tons)
Organic material
(kg/tons)
Deposition holes
8.7 × 104
(with bentonite)
Mean: 1,780
1.6 × 108/1.6 × 105
9.8 × 105/9.8 × 102
Deposition tunnels
1.2 × 106
1,700
2.0 × 109/2.0 × 106
1.2 × 107/1.2 × 143
Main and transport
tunnels
6.4 × 105
1,700
1.1 × 109/1.1 × 106
7.0 × 106/7.0 × 103
Central area
1.19 × 105
–
–
–
Shafts and ramps
(with bentonite)
1.4 ×105
1,700
2.4 × 108/2.4 × 105
1.5 × 106/1.5 × 103
2.2 × 10
–
3.5 × 10 /3.5 × 10
Deposition plugs
Total
4.9 × 104/4.9 ×101
6
9
6
2.2 × 107/2.2 × 104
Table 2‑8. Amount of bentonite and organic material in the Laxemar repository according to
Layout D2.
Area
Theoretical volume
(m3)
Bentonite dry density
(kg m–3)
Amount of bentonite
(kg/tons)
Organic material
(kg/tons)
Deposition holes
8.7 × 104
(with bentonite)
Mean: 1,780
1.6 × 108/1.6 × 105
9.8 × 105/9.8 × 102
Deposition tunnels
1.8 × 106
1,700
3.0 × 109/3.0 × 106
1.9 × 107/1.9 × 104
Main and transport
tunnels
8.9 × 10
1,700
1.5 × 10 /1.5 × 10
9.5 × 106/9.5 × 103
5
9
6
Central area
1.19 × 105
–
–
–
Shafts and ramps
(with bentonite)
1.6 × 105
1,700
2.7 × 108/2.7 × 105
1.7 × 106/1.7 × 103
3.0 × 10
–
4.9 × 10 /4.9 × 10
Deposition plugs
Total
TR-10-19
7.4 ×104/7.4 ×101
6
9
6
3.1 × 107/3.1 × 104
33
2.2
Organic material in underground constructions
2.2.1 Rock support
When opening and constructing the repository, different types of supporting material will be used
to reinforce the construction and maintain worker safety.
To prevent minor spalling, the roof will be supported with shotcrete in all underground cavities
except the deposition area, tunnels, and holes. Rock bolts and wire mesh will be used to provide
additional support; the rock bolts will be secured with grout.
Shotcrete
The composition of the shotcrete used for rock support in Forsmark and Laxemar and the total
amounts of the shotcrete ingredients are summarised in Table 2‑9 and Table 2‑11, respectively, in
terms of both the volume and mass of the various ingredients. Table 2‑10 and Table 2‑12 list the
shotcrete additives together with the active substances and the amounts of organic material.
Shotcrete is assumed to remain on the rock surfaces of the underground cavities. The organic materials
will contribute to the total amount of organic material remaining in the repository.
Concrete in bolt holes
Rock bolts will be fastened with grout. Table 2‑13 and Table 2‑14 summarise the composition of the
grout used in Forsmark and Laxemar, together with the total amounts of the grout additives. If the
bolts are left in the repository, the grout with additives will remain as well. The only organic component of the grout is the superplasticiser Glenium 51 from BASF. Up to 35% of this superplasticiser
consists of polycarbonate ether.
In Forsmark, 2.5 tons of Glenium 51 will be used; with an organic component of 35%, 0.9 tons of
organic material will remain in the rock bolt holes.
From Table 2‑14 it can be seen that in Laxemar, 4.4 tons of the superplasticiser Glenium 51 will be
used in the grout for setting the rock bolts. With an organic fraction of 35% in this additive, this will
add 1.5 tons to the organic pool.
Table 2‑9. The assessed quantities of rock support structural elements in shotcrete in Forsmark
required for the reference design at completion of the final repository facility.
Subsidiary material
Kg m–3
(from SKB)
Ramps/access
area
ton
m3
Central area,
including
ventilation
ton
m3
Deposition area,
including SA01
and SA02*
ton
m3
Water
158
240
240
236
236
768
768
Ordinary Portland cement,
210
319
152
313
149
1,020
486
Silica fume
140
213
101
209
99
680
324
Coarse aggregate, 5–11 mm
552
840
494
823
484
2,682
1,577
1,025
1,559
917
1,528
899
4,979
2,929
250
380
190
373
186
1,215
607
3
4.6
4.6
4.5
4.5
15
15
Air-entraining agent: AER S
(SIKA)
2.5
3.8
3.8
3.7
3.7
12
12
Accelerator: Sigunit (SIKA) or
AF2000 Mapequick (Rescon)
7%
0.1
0.1
0.1
0.1
0.3
0.3
Natural sand, 0–5 mm
Quartz filler (0–0.25 mm) or
limestone filler (0–0.25 mm)
Superplasticiser: Glenium 51
(BASF)
* SA01 and SA02 are exhaust shafts.
34
TR-10-19
Table 2‑10. The amount of organic material in shotcrete additives used in Forsmark.
Organic additive
Total
amount in
deposition
area (tons)
Total
Active component
amount
other areas
(tons)
Part of total
amount (%)
Total organic
additive in
deposition
area (tons)
Total
organic
additive in
other areas
(tons)
Superplasticiser:
Glenium 51 (BASF)
15
9
Polycarboxylate
ether
35
5.2
3.2
Accelarator:
Sigunit (SIKA)
0.3
0.2
Na2CO3
CaCO3
Ca(OH)2
AlNaO2
25–35
25–35
20–25
10–20
–
–
Alternative accelerator:
AF2000 Mapequick
(Rescon)
0.3
0.2
2,2-imino-diethanol
Al2(SO4)3 and other
aluminium salts
5–10
0.015–0.03
0.01–0.02
30–60
–
–
Air-entraining agent:
AER S (SIKA)
12
Sulphonic-acidC14–16-alkanehydroxy and
C14–16-alkenesodium salts
Disodium lauryl
ethoxy sulphosuccinate
Fatty alcohol
(C8–C10) alkyl
glucoside
Fatty acid alcohol
C10–C14
1–5
0.12 –0.6
0.08–0.38
1–5
0.12–0.6
0.08–0.38
1–5
0.12–0.6
0.08–0.38
3–5
0.36–0.6
0.22–0.38
7.5
Table 2‑11. The assessed quantities of rock support structural elements in shotcrete in Laxemar
required for the reference design at completion of the final repository facility.
Subsidiary material
Kg m–3
(from SKB)
Ramps/access
area
ton
m3
Central area,
including
ventilation
ton
m3
Deposition area,
including SA01
and SA02*
ton
m3
Water
158
327
327
372
372
1,197
1,197
Ordinary Portland cement
210
435
207
494
235
1,590
757
Silica fume
140
290
138
329
157
1,060
505
Coarse aggregate, 5–11 mm
552
1,143
672
1,299
764
4,180
2,459
1,025
2,122
1,248
2,412
1,419
7,762
4,566
250
518
259
588
294
1,893
947
3
6.2
6.2
7.1
7.1
23
23
Air-entraining agent: AER S
(SIKA)
2.5
5.2
5.2
5.9
5.9
19
19
Accelerator: Sigunit (SIKA) or
AF2000 Mapequick (Rescon)
(wet weight%)
7%
0.1
0.1
0.2
0.2
0.5
0.5
Natural sand, 0–5 mm
Quartz filler (0–0.25 mm) or
limestone filler (0–0.25 mm)
Superplasticiser: Glenium 51
(BASF)
*SA01 and SA02 are exhaust shafts.
TR-10-19
35
Table 2‑12. The amount of organic material in shotcrete additives used in Laxemar.
Organic additive
Total amount
in deposition
area (tons)
Total
amount
other areas
(tons)
Active component
Part of total
amount (%)
Total organic
additive in
deposition
area (tons)
Total
organic
additive in
other areas
(tons)
Superplasticiser:
Glenium 51 (BASF)
23
13
Polycarboxylate
ether
35
8.0
4.6
Accelarator:
Sigunit (Sika)
0.5
0.3
Na2CO3
CaCO3
Ca(OH)2
AlNaO2
25–35
25–35
20–25
10–20
–
–
Alternative
accelerator: AF2000
Mapequick (Rescon)
0.5
0.3
2,2‑imino‑diethanol
Al2(SO4)3 and other
aluminium salts
5–10
0.03–0.05
0.02–0.03
30–60
–
–
Air-entraining agent:
AER S (SIKA)
19
Sulphonic-acidC14–16-alkanehydroxy-and
C14–16-alkenesodium salts
Disodium lauryl
ethoxy sulphosuccinate
Fatty alcohol
(C8–C10) alkyl
glucoside
Fatty acid alcohol
C10–C14
1–5
0.19–0.95
0.11–0.55
1–5
0.19–0.95
0.11–0.55
1–5
0.19–0.95
0.11–0.55
3–5
0.6–0.95
0.33–0.55
11
Table 2‑13. The assessed quantities of rock support structural elements in bolt holes required for
the reference design at completion of the final repository facility of Forsmark.
Subsidiary material
Kg/m–3
(from SKB)
Ramps/access
area
ton
m3
Central area,
including
ventilation
ton
m3
Deposition area,
including SA01
and SA02
ton
m3
Cement
340
15
7.2
29
13.9
172
82
Silica
226.7
10
4.8
19
9.2
115
54.7
Water
266.6
12
12
23
23
135
135
Glenium 51
4
0.2
0.2
0.3
0.3
2
2
Quartz filler
1,324
118
59
113
56.7
671
335
Table 2‑14. The assessed quantities of rock support structural elements in bolt holes required for
the reference design at completion of the final repository facility of Laxemar.
Subsidiary material
Kg/m–3 (from
SKB)
Ramps/access
area
ton
m3
Central area,
including
ventilation
ton
m3
Deposition area,
including SA01
and SA02
ton
m3
Cement
340
40
19
31
15
301
143
Silica
226.7
26
13
21
10
200
95
Water
266.6
31
31
25
25
236
236
Glenium 51
4
0.5
0.5
0.4
0.4
3.5
3.5
Quartz filler
1,324
154
77
122
61
1,171
585
36
TR-10-19
Total amount of iron in rock support structural elements left in the repository
As described in section 1.8.5, iron can indirectly contribute to the production of organic material and
to sulphate reduction by promoting hydrogen production during anaerobic corrosion. In Forsmark,
the total amount of steel in rock bolts used for rock support is calculated to weigh 402 tons and in
wire mesh to weigh 5.6 tons, giving a total of 407.6 tons of steel (see Table 2‑15). If iron is taken to
comprise 97% of this amount of steel, the total amount of iron will be 395 tons. Rock bolts and wire
mesh are supposed to remain after repository closure in rock walls and in roofs of the underground
cavities.
In Laxemar 1,070 tons of steel will be used for rock support structural elements and left in the
repository at closure (see Table 2‑16). If iron is taken to comprise 97% of this amount of steel, the
total amount of iron will be 1,038 tons.
Hydrogen production from the anaerobic corrosion of steel.
According to the theory described in section 1.8.5, hydrogen will be produced in the oxidationreduction reaction with protons according to Eq. 2-1.
Fe0 + 2H+ → Fe2+ + H2
Eq. 2‑1
The produced hydrogen can then be used as an energy and electron donor by anaerobic microorganisms.
The theoretical maximum quantity of hydrogen that can be produced is equimolar to the amount
of iron. The values for Forsmark and Laxemar are compiled in Table 2‑17, including for partial
hydrogen production if only 50, 10, 1 and 0.1% of the iron oxidises produce hydrogen.
Table 2‑15. The assessed quantities of rock support structural elements required for the
reference design in Forsmark at completion of the final repository facility.
Subsidiary material
Ramps/access
area
ton
Central area,
including
ventilation
ton
Deposition
area, including
SA01 and SA02
ton
Rock bolts (l = 3 m, d = 25 mm, ρ = 4 kg/m )
28
54
320
Wire mesh (1.7 kg/m2)
–
–
5.6
–3
Table 2‑16. The assessed quantities of rock support structural elements required for the
reference design in Laxemar at completion of the final repository facility.
Subsidiary material
Ramps/access
area
ton
Central area,
including
ventilation
ton
Deposition area,
including SA01
and SA02
ton
Rock bolts (l = 3 m, d = 25 mm, ρ = 4 kg/m–3)
73
58
558
Wire mesh (1.7 kg/m2)
–
–
381
Table 2‑17. Calculated theoretical amount of hydrogen that can be produced by anaerobic corro‑
sion of iron in rock support structural elements in the repositories. See text for explanation.
Iron
Site
Hydrogen
100%
Hydrogen
50%
Hydrogen
10%
Hydrogen
1%
Hydrogen
0.1%
Amount of
substance
(mol)
Amount of
substance
(mol)
Amount of
substance
(mol)
Amount of
substance
(mol)
Amount of
substance
(mol)
Amount of
substance
(mol)
395
7.1 × 106
7.1 × 106
3.6 × 106
7.1 × 105
7.1 × 104
7.5 × 103
1,038
1.9 × 107
1.9 × 107
9.5 × 106
1.9 × 106
1.9 × 105
1.9 × 104
Mass
(tons)
Forsmark
Laxemar
TR-10-19
37
Table 2‑18 presents the same calculations for the theoretical production of acetate by acetogenic
bacteria. Values for partial production are also presented, if only 50, 10, 1 and 0.1% of the total iron
amount is anaerobically corroded and the resulting hydrogen is used to produce acetate.
Table 2‑18 presents a range of production values for organic material in the form of acetate. The
highest value is the amount that can be produced if all the iron is corroded, whereas the lowest value
is the amount that will be produced if 0.1% of the iron is anaerobically corroded and the resulting
hydrogen is used for acetate production. Table 2‑19 summarises the theoretical amounts of acetate
produced in the deposition area and elsewhere in the repository.
2.2.2 Grouting
The specifications for the buffer, backfill, and closure state that water inflow because of groundwater
drawdown must be minimised due to the risk of piping erosion and environmental impact. The reference design contains an assessment of the amount of grouting that must be used to meet the inflow
requirements. Pre-grouting, a normal measure in tunnels, shafts, and deposition tunnels, is done concurrently with rock excavation. Transmissive fractures with small apertures may require post-grouting
with silica sol. If the requirements for piping erosion are not fulfilled in a tunnel section, post-grouting
with cement or silica sol is done after rock excavation is completed in the section of concern.
The estimated quantities of grouting material that will remain in the rock after excavation are taken
from the Grouting Report by /Ellison and Magnusson 2009/. Details concerning water flow, drilling,
number of boreholes, etc. are found in this report. Table 2‑20 and Table 2‑21 summarise the composition of grout proposed for different parts of the repositories at Forsmark and Laxemar, respectively.
The only grout additive that contains organic matter is the superplasticiser, which in this case contains naphthalene sulphonate. For Forsmark, calculated using data from Table 2‑20, the total amount
of plasticiser will be between 30 and 120 tons. Between 30 and 50% of the superplasticiser is the
active component, i.e. polymerised naphthalene sulphonate. With a 30% content, the total amount of
polymerised naphthalene sulphonate can vary from 9 to 36 tons and with a 50% content, from 15 to
60 tons. Consequently, the total quantity of naphthalene sulphonate could vary from 9 to 60 tons,
depending on the need for grouting in the underground cavities.
Table 2‑18. Calculated theoretical amount of acetate that can be microbially produced from
hydrogen produced by anaerobic corrosion of iron in rock support structural elements in the
repositories. See text for explanation.
Iron
Site
Forsmark
Laxemar
Acetate
100%
Acetate
50%
Acetate
10%
Acetate
1%
Acetate
0.1%
Amount of
substance
(mol)
Amount of
substance
(mol)/mass
(tons)
Amount of
substance
(mol)/mass
(tons)
Amount of
substance
(mol)/mass
(tons)
Amount of
substance
(mol)/mass
(tons)
Amount of
substance
(mol)/mass
(tons)
395
7.1 × 106
1.8 × 106/
1.0 × 102
9 × 105/
0.55 × 102
1.8 × 105/
1.1 × 101
1.8 × 104/
1.1
1.8 × 103/
0.11
1,038
1.9 × 107
4.75 × 106/
2.8 × 102
2.4 × 102/
1.43 × 102
4.75 × 105/
2.85 × 101
4.75 × 104/
2.85
4.75 × 103/
0.285
Mass
(tons)
Table 2‑19. Theoretical amounts of acetate produced from 100% corrosion of iron in rock support
structural elements.
Forsmark
Laxemar
Deposition
holes (tons)
Deposition
tunnels (tons)
Other areas
(tons)
Deposition
holes (tons)
Deposition
tunnels (tons)
Other areas
(tons)
–
84
21
–
245
34
Percentage of
iron corroded
100%
38
TR-10-19
Table 2‑20. Estimated quantities of grout materials and extent of drilling remaining in the rock
mass after excavation of the various underground cavities in Forsmark.
Element
Cement grouting
Material
Deposition area
Min
Max
Water
350
1,360
3
10
110
440
330
1,310
3
8
100
400
Silica fume3)
460
1,790
4
11
140
550
23
90
0.2
0.5
7
30
105
410
3
9
160
640
21
85
0.6
2
30
130
910
3,580
10
30
405
1,620
Silica
NaCl solution
Volume of grout (m3)
Drilling
Central area
(tons)
Min
Max
Portland cement2)
Superplasticiser 4)
Chemical grouting
Ramps/shafts
(tons)1)
Min
Max
Number of holes
Drilling length (km)
7,980
300
17,160
205
6
343
Including exhaust shafts SA01 and SA02.
Sulphate-resistant ordinary Portland cement with d95 on 16-µm type.
3)
Dispersed silica fume, microsilica with d90 = 1-µm type. The density is to be 1,350–1,410 kg m3 and 50% ± 2% of the
solution is to consist of solid particles.
4)
Superplasticiser, naphthalene sulphonate based, density approximately 120 kg/m3
1)
2)
Table 2‑21. Estimated quantities of grout materials and extent of drilling remaining in the rock
mass after excavation of the various underground cavities in Laxemar.
Element
Cement grouting
Material
Water
Portland cement2)
Silica fume3)
Superplasticiser 4)
Chemical grouting
Silica
NaCl solution
Volume of grout (m3)
Drilling
Number of holes
Drilling length (km)
Ramps/shafts
(tons)1)
Min
Max
Central area
(tons)
Min
Deposition area
Max
Min
Max
2,500
120
470
40
120
620
90
360
30
85
540
2,200
120
490
40
120
740
3,000
6
25
2
6
40
150
110
420
40
110
4,000
16,000
20
80
8
20
790
3,200
350
1,400
120
350
5,000
20,500
8,900
5,100
180,000
220
100
3,700
Sulphate-resistant ordinary Portland cement with d95 on 16-µm.
Dispersed silica fume, microsilica with d90 = 1-µm. The density is to be 1,350–1,410 kg/m3 and 50% ± 2% of the
solution is to consist of solid particles.
3)
Superplasticiser, naphthalene sulphonate based, density approximately 120 kg/m3.
1)
2)
Similar estimates of the amount of organic material in grout in Laxemar can be made using data
from Table 2‑21. The total amount of plasticiser will be between 48 and 181 tons. Between 30 and
50% of the superplasticiser is the active component, i.e. polymerised naphthalene sulphonate. With
a 30% content, the total amount of polymerised naphthalene sulphonate can vary from 14 to 54 tons
and with a 50% content, from 24 to 90 tons. Thus, in Laxemar, the total quantity of naphthalene
sulphonate in grout could vary from 14 to 90 tons depending on the need for grouting in the
underground cavities.
TR-10-19
39
2.3
Foreign and stray organic material left in the repository
Apart from construction material, other organic material will remain in the repository at the time of
closure. Estimates of the remaining amounts of various stray materials are found in /Lindgren et al.
2009a, b/, respectively. The routines and methods to be used to remove the installations and constructions and to clean the deposition tunnels and other rock cavities have not yet been determined,
making it difficult to estimate the remaining amounts of materials. There will be restrictions on how
much foreign material can be left, especially in the deposition tunnels. In most cases, a level of 1%
of the used material is used in estimating the amount of material remaining at time of closure. Here,
only the estimated amounts of stray material that can contribute to the pool of organic material are
compiled and the possibility of biodegradation is discussed.
2.3.1 Organic materials in stray material left in the repository
Tables 2‑23 and 2‑24 compile all the estimated amounts of foreign material that could be left in the
repository. A short summary of the materials is presented below. A more detailed description of the
material and the calculations underlying the estimated quantities are found in the background reports
/Lindgren et al. 2009a, b/.
Table 2‑22 present the amount of organic material that will be left in the repository. In the case of
iron, the total amount is presented, and not recalculated as related organic material. The repositories
are divided into the deposition area, i.e. the deposition holes and tunnels, and other areas, i.e. the
main and transport tunnels, central area, ramps, and shafts.
Plastics
Some plastic residues will come from detonators, mostly from the polypropylene coating of the
electric cables. The estimates are made assuming that 1% of the used material will be left in the
repository at closure.
Anchoring bolts
Anchoring bolts are used for ventilation channels, tubes, and cables. These are made of steel, which
is 97% iron. In the deposition area, the bolts will be of an expander type that can be removed at
closure. In the other areas, the bolts will be attached to the rock wall with grout. It is calculated that
0.5 kg of each 2‑kg bolt will remain at closure.
The organic material in concrete is the added superplasticiser, which is suggested to be Glenium 51
(BASF). Its main component is modified polycarboxylate ether and it is added at a rate of 4 kg/m3 or
0.4% by volume of the concrete; 35% of Glenium 51 consists of the active organic compound.
Table 2‑22. The amount of organic material in foreign material left in the repositories in Forsmark
and Laxemar at closure.
Total amount (kg)
Forsmark
Laxemar
Deposition area
Polypropylene
Other areas
Deposition area
Other areas
100
130
100
0
81
0
97
4.8 × 104
6.8 × 104
7.6 × 104
9.0 × 104
Modified lignin sulphonate
0
7
0
10
Polycarboxylate ether
4
5
4
7
Bitumen
0
30
0
36
Polycarboxylate ether
Iron
Rubber
82
2
14
2
14
200
80
360
110
Urea
6
2
6
2
Wood
10
4
10
4
Organic materials in human waste
60
19
60
19
Organic materials from ventilation
10
8
10
8
Hydraulic and lubrication oil
40
TR-10-19
TR-10-19
Table 2‑23. Total quantity of foreign material left in the Forsmark repository.
Material
Amount of foreign material left in the Forsmark repository after closure (kg)
Deposition holes
Deposition tunnels
Main and transport
tunnels
Central area
Ramps and shafts
Total quantity
*
3 × 101
1 × 101
3
5
4.8 × 101
2.3× 102
Detonators with
cables
Zinc
Plastics
*
1 × 102
8 × 101
2 × 101
3 × 101
Explosives
NOx
*
7
4
1
2
1.4 × 101
Nitrate salts
*
2 × 103
1 × 103
2 × 102
4 × 102
3.6 × 103
Steel
*
5 × 104
4 × 104
1 × 104
2 × 104
1.2 × 105
Concrete
0
0
3 × 104
8 × 103
2 × 104
5.8 × 104
Concrete
0
0
2 × 103
6 × 102
1 × 103
3.6 × 103
Asphalt**
0
0
0
0
5 × 102
5 × 102
Concrete
*
3 × 103
2 × 103
6 × 102
1 × 103
6.6 × 103
*
1.5
8.5
1.7
3.4
5.1 × 101
*
7
3 × 10
9
2 × 10
0
0
0
0
0
*
2 × 102
5 × 101
1 × 101
2 × 101
2.8 × 102
*
Anchoring bolts
Roads
Concrete
constructions
Tyres
Exhaust
NOx
Particles
Hydraulic and
lubricating oil
2
1
3.36 × 102
Diesel
*
*
*
*
*
Battery acid
*
*
*
*
*
*
Metal chips and
hard metal
*
5
1
0.3
1
7.3
1.4 × 101
Wooden chips
Wood
*
10
2
1
1
Corrosion products
Rust
*
4 × 103
184
50
95
4.3 × 103
Urine
Urea
*
6
1
0
1
8
Other human waste
Organic materials
*
6 × 101
1 × 101
3
6
7.9 × 101
Ventilation air
Organic materials
*
10
5
1
2
1.8 × 101
* Limited amounts, difficult to quantify.
** Asphalt will only be present in the ramps.
41
42
Table 2‑24. Total quantity of foreign material left in the Laxemar repository.
Material
Amount of foreign material left in the Laxemar repository after closure (kg)
Deposition holes
Deposition tunnels
Main and transport
tunnels
Central area
Ramps and shafts
Total quantity
Zinc
*
8
4
1
1
1.4 × 101
Plastics
*
1 × 102
60
8
1.7 × 101
1.8 × 102
Explosives
NOx
*
10
6
1
2
1.9 × 101
Nitrate salts
*
3 × 103
2 × 102
2 × 102
5 × 102
3.9 × 103
Anchoring bolts
Steel
*
8 × 104
6 × 104
1 × 14
2 × 104
1.7 × 105
Concrete
0
0
4 × 104
8 × 103
2 × 104
6.8 × 104
Concrete
0
0
3 × 103
6 × 102
1 × 103
4.6 × 103
Asphalt**
0
0
0
0
6 × 102
6 × 102
Concrete
*
2 × 103
3 × 103
6 × 102
1 × 103
6.6 × 103
*
2
8
2
3
1.5 ×101
NOx
*
10
60
11
24
1.05 × 102
Particles
Detonators with
cables
Roads
Concrete
constructions
Tyres
Exhaust
*
0.1
1
0.1
0.3
1.5
Hydraulic and
lubricating oil
*
4 × 102
70
10
30
5.1 × 102
Diesel
*
*
*
*
*
*
Battery acid
*
*
*
*
*
*
Metal chips and
hard metal
*
8
2
0.3
0.6
1.1 ×101
0.4
0.8
50
1 × 10
Wooden chips
Wood
*
10
Corrosion products
Rust
*
6 × 10
2
3
2 × 10
2
1.3 ×101
2
6.4 × 103
Urine
Urea
*
6
1
0.2
0.5
8
Other human waste
Organic materials
*
61
11
2
5
7. 9 ×101
Ventilation air
Organic materials
*
11
5
0.8
2
1.9 ×101
* Limited amounts, difficult to quantify.
** Asphalt will only be present in the ramps.
TR-10-19
Roads
It is suggested that the roads in the deposition tunnels be made of macadam; these roads will be
removed before closure. Neither concrete nor asphalt will be used in this area.
The ramps, transport tunnels, main tunnel, and central area will have roads paved with concrete,
which should be removed. As the concrete will be placed on a bed of macadam, it should be
possible to remove almost all the concrete at closure. Some small pieces and dust will be left and
it is assumed that 0.01% of the road concrete will remain. The roads on the ramps will be asphalt
paved. These roads will also be removed, and it is estimated that 0.01% of this asphalt will remain
at closure. The organic fraction of asphalt is 6% bitumen, the rest being macadam.
Concrete constructions
Minor amounts of concrete will remain from constructions built to facilitate drilling and deposition of
the canisters. It is estimated that 0.01% of this concrete will remain at closure. The organic fraction of
the concrete is the superplasticiser, which is suggested to be Glenium 51 (as in the concrete used with
the anchoring bolts). Its main component is modified polycarboxylate ether and it is added at a rate of
4 kg/m3 or 0.4% by volume of concrete; 35% of Glenium 51 consists of the active organic compound.
Wear of tyres
A very limited amount of rubber from tyres will remain in the repository, since most of the particles
and dust will be pumped out with the drainage water. It is assumed that 1% of the calculated total
amount of particles and dust from tyres will remain in the deposition tunnels and other tunnels and
areas.
Emissions from diesel engines
The exhaust from diesel engines consists mostly of carbon dioxide and water, but also contains some
particles, soot, and nitrogen oxides. It is calculated that approximately 1% of these total diesel-related
emissions of particles and nitrogen oxides will remain in the repository.
Detergents and degreasing agents
The detergents and degreasing agents will mostly be used in the central area, and there will be systems
to take care of the waste. There will be no spills of these materials during normal operations and only
limited amounts will remain at closure.
Hydraulic and lubrication oil
Many vehicles and machines used in construction and waste deposition incorporate hydraulic equipment. Breakage of hydraulic tubes is relatively common during use and repairs. To minimise spillage
of hydraulic oil, it is possible to:
• equip machines with containers for collecting spilt oil,
• absorb larger spills from drilling machines using absorbant material,
• use biodegradable oils based on rapeseed oil.
It is calculated that 1% of the spilt oil will remain by the time of closure.
Diesel
Spills of diesel can occur from leaking fuel tanks, tubes, and pumps in vehicles and when refuelling
vehicles. Refuelling will be done in the central area at a tank station equipped with an oil separator
and flooding protection. Diesel spills in other areas will probably be pumped out with the drainage
water. Overall, only a minor amount of diesel will remain in the repository.
TR-10-19
43
Metal chips and hard metal
The most important components of hard metal are bismuth carbide and cobalt. Residues of hard steel
will come mainly from drilling machines and excavators. Most of it will be drained out with the
drainage water and it is assumed that 1% will remain. This amount will not contribute any organic
material of significance to the repository.
Wooden chips
Wooden chips from construction work will remain on the floor and in the rock debris (“syltan”). Most
of them will be drained out with drainage water, and it is calculated that 1% of the wood will remain.
Organic material from human activities
Urea
Due to restrictions on urination in the repository area, only a minor amount of urea will remain. Most
of any urine will be drained out; since the nitrogen of urea is a major nutrient for microorganisms, it
will probably be readily consumed during the operational phase of the repository.
Other human waste
This is assumed to consist mostly of snuff mixed with saliva. There should of course be restrictions
concerning spitting snuff in the tunnels. Calculations in /Lindgren et al. 2009a, b/ assume that all the
snuff used will be spat out in the tunnel and that most of this will be pumped out with the drainage
water. The amount of organic material in the “other human waste” is calculated assuming that 1% of
the material will remain at repository closure.
Ventilation
Regarding organic material, it is assumed that 1% of the particles in the ventilation air will remain in
the repository. Only part of this consists of organic material, such as spores.
2.4
Organic material in microbial biofilms
In Table 2‑25 and Table 2‑27, the surface areas of the different parts of the Forsmark and Laxemar
repositories are presented, respectively. If it is assumed that microbial biofilms will grow on approximately 5% of the wall and ceiling area, Table 2‑26 and Table 2‑28 present the calculated amounts
of organic material in such biofilms in the Forsmark and Laxemar repositories, respectively. This is
an estimation based on experiences from work in tunnel environments by the author. This factor is
difficult to define with confidence because it differs between the groundwater environments and is
also due to the cleaning of walls and ceiling before closure of the repository. The true factor has to
be determined during the construction phase
Table 2‑25. Dimensions of the repository based on layout D2, Forsmark.
Deposition
tunnels
Main and transport
tunnels
Central area
Access ramp
Width (m)
10
8.5 (mean value)
6.5 (mean value)
5.5
Height (m)
4.8
6.3 (mean value)
5.5 (mean value)
6
Length (m)
52,200
10,700
2,900
4,700
Total area (without roadways) (m2)
1,023,000
257,800
50,750
82,300
5% of the total area (m )
51,100
11,300
2,500
4,100
2
44
TR-10-19
Table 2‑26. Organic material in a 1-mm-thick biofilm of varied density in Forsmark.
Density 10 (kg/m–3)
Organic material: 10 g m–2
Density 25 (kg/m–3)
Organic material: 25 g m–2
Density 75 (kg/m–3)
Organic material: 75 g m–2
Deposition tunnels (kg)
511
1,278
Main and transport tunnels (kg)
113
282
3,833
848
Central area (kg)
25
62
188
Access ramp (kg)
Total amount (kg)
41
690
102
1,724
308
5,180
Table 2‑27. Dimensions of the repository based on layout D2, Laxemar.
Deposition
tunnels
Main and transport
tunnels
Central area
Access ramp
Width (m)
10
8.5 (mean value)
6.5 (mean value)
5.5
Height (m)
4.8
6.3 (mean value)
5.5 (mean value)
6
4,700
Length (m)
80,400
14,800
2,900
Total area (without roadways) (m2)
1,576,000
312,280
50,750
82,300
5% of the total area (m2)
78,800
15,600
2,500
4,100
Table 2‑28. Organic material in a 1-mm-thick biofilm of varied density in Laxemar.
Density 10 (kg/m–3)
Organic material: 10 g m–2
Density 25 (kg/m–3)
Organic material: 25 g m–2
Density 75 (kg/m–3)
Organic material: 75 g m–2
Deposition tunnels (kg)
788
1,970
5,910
Main and transport tunnels (kg)
156
390
1,170
188
Central area (kg)
25
62
Access ramp (kg)
41
102
308
Total amount (kg)
1,010
2,524
7,576
2.5
Estimates of the amounts of organic material left in the
repository system
2.5.1
Estimates of the total amounts of organic material in buffer, backfill,
rock-support structural elements, and grouting
Table 2‑29 presents the total amounts of organic material contained in buffer, backfill, rock-support
structural elements, and material used in tunnel construction and grouting in both sites. For steel,
a maximum corrosion scenario is assumed and the produced hydrogen gas is recalculated to acetate
synthesised by microorganisms as described in section 1.8.5. The table is divided according to the
three different areas of the repository:
1. the deposition holes,
2. the deposition tunnels,
3. other areas.
“Other areas” include transport and main tunnels, the central area, ramps, and shafts. The bentonite is
the major source of organic material in all areas. (See discussion below on the likelihood of dissolution of this material). The second largest source is the superplasticiser in shotcrete.
TR-10-19
45
Table 2‑29. Organic material in buffer, backfill, rock-support structural elements, and grouting.
Forsmark
Laxemar
Deposition
holes (tons)
Deposition
tunnels (tons)
Other areas
(tons)
Deposition
holes (tons)
Deposition
tunnels (tons)
Other areas
(tons)
9.8 × 102
1.2 × 104
8.5 × 103
9.8 × 102
1.9 × 104
1.2 × 104
super-plasticiser
–
5.2
3.2
–
8.0
4.6
alternative accelerator
–
0.02–0.03
0.01–0.02
–
0.03–0.05
0.02–0.03
air-entraining agent
–
<2.4
<1.5
<3.8
<2.2
super-plasticiser
–
0.7
0.2
–
1.2
0.32
acetate from iron
corrosion*
–
0.084–84
0.02–21
–
0.24–240
0.03–34.2
–
2.1–9.0**
3.5–15***
7.0–27**
12–45***
–
12–18**
20–75***
2.4–4**
9.3–16***
Buffer and backfill:
Bentonite
Rock support:
Shotcrete:
Rock bolts:
Grouting:
super-plasticiser
* See section 1.8.5
** With 30% of the active component
*** With 50% of the active component
2.5.2
Estimates of the total amounts of organic material in foreign material in
the repository
Table 2-30 presents the total amounts of organic material originating from so-called foreign material.
The organic material from steel is calculated as acetate produced by microorganisms (see section 1.8.5).
None of this material is to remain in the deposition holes.
2.5.3 Calculations of water volumes in the repository
To calculate the concentrations of various organic materials in a closed and water-saturated repository, the porosities of the different backfill materials must be estimated. The void ratio, e, is related
to the porosity, ø, by the following equation:
ø = e (1 + e)–1
Eq. 2‑2
Porosity is described as the fraction of the void space included in the material and is defined by the
following ratio:
ø = Vv / VT
Eq. 2‑3
where Vv is the volume of void space and VT is the total or bulk volume of material including the
solid and void components.
Table 2‑31 and Table 2‑32 present the calculated volumes of water in the different areas of the
repositories in Forsmark and Laxemar, respectively. The background information comes from /Pusch
2008/.
Since the intention is to fill the central area and upper part of the ramp with crushed rock having
a Fuller-type size distribution, which allows for the most effective compaction of the material, the
lowest porosity of crushed rock cited by /Pusch 2008/ was used in the water volume calculations for
these areas.
It is assumed that 82% of the volume is filled with bentonite blocks and 17% is filled with pellets in
the deposition tunnels, and this proportion is also used for the shafts and ramps. Of the total volume
of the shafts and ramps, 2.45 × 105 m3, 1.4 × 105 m3 will be filled with bentonite. Of this volume,
1.1 × 105 m3 will be filled with blocks and 2.4 × 104 m3 with pellets.
46
TR-10-19
Table 2‑30. Organic material in stray material to be left in the repository.
Forsmark
Laxemar
Deposition
holes (tons)
Deposition
tunnels (tons)
Other areas
(tons)
Deposition
holes (tons)
Deposition
tunnels tons)
Other areas
(tons)
–
0.10
0.13
–
0.10
0.08
Steel**
–
0.013–13
0.018–18
–
0.020–20
0.023–23
Concrete
–
–
0.08
–
–
0.1
Concrete
–
–
0.01
–
–
0.01
Asphalt
–
–
0.03
–
–
0.04
–
0.003
0.005
–
0.002
0.007
Rubber
–
*
*
*
*
Particles
–
*
*
*
*
Hydraulic and
lubrication oil
–
0.2
0.08
–
0.36
0.11
Metal chips**
–
*
*
–
*
*
Wooden chips
–
0.01
0.004
–
0.01
0.004
–
0.006
0.002
–
0.006
0.002
–
0.06
0.02
–
0.06
0.02
–
0.001
0.008
–
0.001
0.007
Detonators
Plastics
Anchoring bolts
Roads
Concrete
constructions
Concrete
Tyres
Urine
Urea
Other human waste
Organic materials
Ventilation air
Organic materials
* Negligible amount.
** See section 1.8.5 for calculations.
Table 2‑31. The calculated volumes of water to fill the areas in the Forsmark repository,
assuming total saturation for the different backfill concepts under study.
Backfill material
Void ratio
Porosity
Total rock volume (m3)
Water volume (m3)
Deposition tunnels
Bentonite:
blocks,
pellets
Total
0.35
1.45
0.259
0.592
82%: 9.8 × 105
17%: 2.0 × 105
1.2 × 106
2.5 × 105
1.2 × 105
Main and
transport tunnels
Bentonite:
blocks,
pellets
Total
0.35
1.45
0.259
0.592
82%: 5.2 × 105
17%: 1.1 × 105
6.4 × 105
1.3 × 105
6.5 × 104
Central area
Crushed rock
0.54
0.350
1.36 × 105
4.8 × 104
Shafts and ramps
Bentonite:
blocks
pellets
Crushed rock
Total
0.35
1.45
0.54
0.259
0.592
0.35
1.4 × 105
2.4 × 104
1.05 × 105
2.45 × 105
3.6 × 104
1.4 × 104
3.7 × 104
Total volume of water
TR-10-19
7.0 × 105
47
Table 2‑32. The calculated volumes of water to fill the areas in the Laxemar repository, assuming
total saturation for the different backfill concepts under study.
Backfill material
Void ratio
Porosity
Total rock volume (m3)
Water volume (m3)
Deposition tunnels
Bentonite:
blocks
pellets
Total
0.35
1.45
0.259
0.592
82%: 1.5 × 106
17%: 3.1 × 105
1.8 × 106
3.9 × 105
1.8 × 105
Main and transport
tunnels
Bentonite:
blocks,
pellets
Total
0.35
1.45
0.259
0.592
82%: 7.3 × 105
17%: 1.5 × 105
8.9 × 105
1.9 × 105
8.9 × 104
Central area
Crushed rock
0.54
0.350
1.36 × 105
4.8 × 104
Shafts and ramps
Bentonite:
blocks,
pellets
Crushed rock
Total
0.35
1.45
0.54
0.259
0.592
0.35
1.3 × 105
2.7 × 104
1.0 × 105
2.66 × 105
3.4 × 104
1.6 × 104
3.5 × 104
Total volume of water
2.6
9.8 × 105
Evolution with time: degradation processes
Of the stray material in a repository, the main organic compounds left are carbohydrates and hydrocarbons. The presence of water is crucial for all degradation processes. When the bentonite has gained its
eventual swelling pressure, the flow of water will decline dramatically over the areas where the stray
materials will be found. The exception is compounds that are water soluble and have been transported
with the groundwater flow during the construction and filling-up of the repository. Most of the
degradation will occur over the first 100 years. Below follows a description of each group of material.
2.6.1 Organic material in bentonite
Most of the organic material left in the repository will be the organic material in bentonite. There are
difficulties finding information about the composition of this material. /Stevenson 1994/ states that
humic substances can be retained by clay minerals in two different ways:
1. by attachment to clay mineral surfaces, such as through cation and anion exchange, bridging by
polyvalent cations (clay-metal-mineral-humus), H-bonding, or van der Waals force,
2. by penetration into the interlayer spaces of expanding-type clay minerals.
Most of the organic material in bentonite clay is probably very closely attached to the clay, so when
the clay has reached its swelling pressure, very little of the organic material will be available for
dissolution into the groundwater.
The release of organic materials from bentonite could increase if the bentonite loses its swelling
properties due to changes in the chemical environment (e.g. a large decrease in salinity or a major
pH change) or in physical conditions (e.g. freezing). In such cases, the organic materials in bentonite
could become more soluble in the groundwater and thus more available for microbial degradation.
2.6.2 Concrete additives
There are several reports of the leakage of additives, mostly plasticisers or superplasticisers, from
concrete. Most such leakage will occur as the non-polymerised monomers of the plasticisers. Many
of the different types of additives are degraded by microorganisms, at least in the initial stages of
degradation, but can also be degraded to complete mineralisation. Most relevant studies have been
done under aerobic conditions. Since grouting will be ongoing during construction, the environment
near the tunnel wall will be aerobic; very soon after repository closure, however, the groundwater
will become anaerobic.
Any degradation of concrete additives will occur early on, from the time of construction to 100 years
after repository closure, and then mainly of the monomers of these substances.
48
TR-10-19
2.6.3
Degradation of carbohydrates
Urea
As described in section 1.15.4, urea will very rapidly be hydrolysed and degraded into ammonium
and carbon dioxide. The degradation process starts immediately and the ammonium will be consumed by microorganisms. By the time of closure, only a small fraction will be left, which will be
degraded within a period of weeks to months.
Other human waste
Materials such as hair, skin, fibres from clothes, and some snuff are included here. These materials
will be disposed randomly in small amounts and will thus have a large surface area. These materials
are biologically degradable and their decomposition will start immediately. By the time of closure,
only a small amount will be left, which will be degraded in approximately 1–5 years.
Organic materials from ventilation
These materials are small-sized particles with a large surface area to volume ratio, which enhances
degradation. These materials are mostly biological in origin and will be degraded in approximately
1–5 years.
Wooden chips and sawdust
The degradation of wood is dependent on specialised fungi and oxygen. Larger pieces are more
difficult to degrade because of their small surface area to volume ratio. There are several examples
of wood that has been preserved for very long time. One extreme example is the wood of the
Dunarobba “fossil forest” in Italy, which is 1.5 million years old. This wood was buried in sediment
and clay, which protected it from degradation, presumably by reducing the flow of water and thereby
the transport of electron acceptors and nutrients. Another example is mosses. In mosses in Sweden,
intact wood can be found that has been deeply buried for up to several thousand years. This is
because no electron acceptors other than carbon dioxide have been present so no degradation has
occurred. Carbon dioxide can only be used as an electron acceptor by methanogens and acetogens,
and they cannot use long-chained carbohydrates as a substrate.
A situation of almost no water transport is comparable to that of the repository once the bentonite clay
is fully saturated. How long wood can remain intact depends on the function of the bentonite; if there
is no water flow, wood can persist for hundreds of thousands of years.
One group of compounds present in wood is the degradation-resistant tannins (see section 1.9.4).
Their molecular structure includes many hydroxyl groups, making them possible complexing agents.
2.6.4
Degradation of hydrocarbons
Plastics
The degradation of plastic depends greatly on the size of the pieces. Small pieces and dust of plastic
will be degraded faster than large pieces due to their large surface area to volume ratio. Other important factors affecting plastic degradation are water flow and thus the transport of nutrients and electron
acceptors. Plastic degradation will be fast during the operational phase of the repository, because of
available flowing water and oxygen. Plastics left near bentonite in the closed and saturated repository
will probably remain intact for several thousand years.
Rubber
Rubber is even less degradable than plastic. Residues of rubber dust from tyres will be minimal, and
degradation in groundwater will probably be negligible. Any degradation that does occur will, like
all other degradation processes, be dependent on flowing water. Rubber left surrounded by or near
bentonite will probably remain intact for several thousand years.
TR-10-19
49
Hydraulic and lubrication oils
These compounds are more soluble in water than are plastics or rubber, although their solubility is
low. During the operational phase and the first years after closure when water is flowing and oxygen is
present, degradation of hydraulic and lubrication oils will occur, especially if biodegradable types are
used. In addition, degradation will occur under anaerobic conditions as long as there is flowing water.
Asphalt
The more soluble compounds in asphalt will degrade as long as water is flowing in the repository.
Most of the heavy hydrocarbons will remain in the asphalt and not degrade for several thousand years.
2.6.5
Time scale for the degradation of organic materials in the deposition
tunnels in Forsmark and Laxemar
Estimations of the degradation of organic materials have been made by classifying the different types
of organic substances according to the following categories: organic materials in buffer, backfill,
and construction material; organic materials in construction materials classified as foreign; and
carbohydrates and hydrocarbons in stray material. For the purposes of the estimations, the repository
has been divided into two areas:
Deposition holes: Since the expected amounts of these chemical substances in stray materials in the
deposition holes are negligible or limited and not quantified, they are disregarded here.
Deposition tunnels and other areas: The total potential volume of water assumed to fill the deposition tunnel cavities (see Table 2‑31 and Table 2‑32) have been calculated by taking into account both
the total volume of these systems and the total porosity of the different backfill concepts.
From information given in sections 2.1.8, 2.5.1, and 2.5.2, it is possible to calculate the expected
amounts of construction and grouting material and stray materials likely to remain in the deposition
tunnels classified according to three categories (i.e. carbohydrate, hydrocarbons, and surface active
substances), together with their estimated concentrations (in kg/m3). They include:
• carbohydrate substances from humus, wooden chips, ventilation air, and human wastes,
• hydrocarbons from, for example, oils, degreasing compounds, plastics, and rubber.
Table 2‑33 to 2‑47 present the estimated amounts of various materials remaining in the repository
after degradation for up to 120,000 years.
In the case of carbohydrates, it is assumed that compounds that can degrade will do so over the first
100 years, if there is enough flowing water. Any remaining compounds will probably still remain
after 120,000 years.
Table 2‑33. Estimated amounts of organic material from buffer, backfill, and construction material
remaining after different periods in deposition tunnels in Forsmark.
Compound
Amounts left
(tons)
Left after
100 years
(tons)
Left after
1,000 years
(tons)
Left after
10,000 years
(tons)
Left after
120,000 years
(tons)
Left
(tons)
Bentonite:
humic and
fulvic acids*
5.0 × 103
?
?
?
?
?
Concrete
additives
<8.3
<7.5
<7.5
<7.5
<7.5
<7.5
Acetate from
anaerobic steel
corrosion**
0.08–84
0
0
0
0
0
* No assumption because of limited knowledge of the organic materials in bentonite.
** Assuming 0.1–100% corrosion of the iron.
50
TR-10-19
Table 2‑34. Estimated amounts of organic material from construction material classified as
foreign, remaining after different periods in deposition tunnels in Forsmark.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Concrete
additives
3
2.7
2.7
2.7
2.7
2.7
Asphalt:
bitumen
–
–
–
–
–
–
Acetate from
anaerobic steel
corrosion
13–1.3 × 104
0
0
0
0
0
Table 2‑35. Estimated amounts of carbohydrate material remaining after different periods in
deposition tunnels in Forsmark.
Compound
Urea
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
6
0
0
0
0
0
Other human
waste
60
0
0
0
0
0
Organic materials
from ventilation
10
0
0
0
0
0
Wooden chips
and sawdust
10
7.5
5.0
5.0
5.0
5.0
Table 2‑36. Estimated amounts of degraded hydrocarbon material remaining after different
periods in deposition tunnels in Forsmark.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Plastics
100
100
100
50
50
Rubber
*
*
*
*
*
*
200
100
0
0
0
0
Hydraulic and
lubrication oil
50
Table 2‑37. Estimated amounts of organic material from buffer, backfill, and construction material
remaining after different periods in deposition tunnels in Laxemar.
Compound
Amounts left
(tons)
Left after
100 years
(tons)
Left after
1,000 years
(tons)
Left after
10,000 years
(tons)
Left after
120,000 years
(tons)
Left
(tons)
Bentonite*:
humic and
fulvic acids
1.9 × 104
?
Concrete
additives
<13
<12
<12
<12
<12
<12
Acetate from
anaerobic steel
corrosion**
0.24–2.4 ×
102
0
0
0
0
0
* No assumption because of limited knowledge of the organic materials in bentonite.
** Assuming 0.1–100% corrosion of the iron.
TR-10-19
51
Table 2‑38. Estimated amounts of organic material from construction material classified as
foreign remaining after different periods in deposition tunnels in Laxemar.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Concrete
additives
2
1.8
1.8
1.8
1.8
1.8
Asphalt:
bitumen
–
–
–
–
–
–
Acetate from
anaerobic steel
corrosion
20–2 × 104
0
0
0
0
0
Table 2‑39. Estimated amounts of carbohydrate material remaining after different periods in
deposition tunnels in Laxemar.
Compound
Urea
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
6
0
0
0
0
0
Other human
waste
60
0
0
0
0
0
Organic materials
from ventilation
11
0
0
0
0
0
Wooden chips
and sawdust
10
7.5
5.0
5.0
5.0
5.0
Table 2‑40. Estimated amounts of hydrocarbon material remaining after different periods in
deposition tunnels in Laxemar.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Plastics
100
100
100
50
50
Rubber
*
*
*
*
*
*
360
180
0
0
0
0
Hydraulic and
lubrication oil
50
Table 2‑41. Estimated amounts of organic material from buffer, backfill, and construction material
remaining after different periods in other areas in Forsmark.
Compound
Amounts left Left after
(tons)
100 years
(tons)
Left after
1,000 years
(tons)
Left after
10,000 years
(tons)
Left after
120,000 years
(tons)
Left
(tons)
Bentonite**:
humic and
fulvic acids
8.5 × 103
Concrete
additives
<5
<4.5
<4.5
<4.5
<4.5
<4.5
Acetate from
anaerobic steel
corrosion*
0.02–21
0
0
0
0
0
* No assumption because of limited knowledge of the organic materials in bentonite.
** Assuming 0.1–100% corrosion of the iron.
52
TR-10-19
Table 2‑42. Estimated amounts of organic material from construction material classified as
foreign remaining after different periods in other areas in Forsmark.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Concrete
additives
90
81
81
81
81
81
Asphalt:
bitumen
30
25
20
15
15
15
Acetate from
anaerobic steel
corrosion
18–1.8 × 104
0
0
0
0
0
Table 2‑43. Estimated amounts of carbohydrate material remaining after different periods in other
areas in Forsmark.
Compound
Amounts left
(kg)
Urea
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
2
0
0
0
0
0
20
0
0
0
0
0
Organic materials
from ventilation
1
0
0
0
0
0
Wooden chips and
sawdust
10
3
2
0
0
0
Other human
waste
Table 2‑44. Estimated amounts of degraded hydrocarbon material remaining after different
periods in other areas in Forsmark.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Plastics
130
130
130
65
65
Rubber
*
*
*
*
*
*
80
40
0
0
0
0
Hydraulic and
lubrication oil
65
Table 2‑45. Estimated amounts of organic material from buffer, backfill, and construction material
remaining after different periods in other areas in Laxemar.
Compound
Amounts left
(tons)
Left after
100 years
(tons)
Left after
1,000 years
(tons)
Left after
10,000 years
(tons)
Left after
Left
120,000 years (tons)
(tons)
Bentonite*:
humic and fulvic
acids
1.2 × 104
?
Concrete
additives
7
6
6
6
6
6
Acetate from
anaerobic steel
corrosion**
0.03–34
0
0
0
0
0
* No assumption because of limited knowledge of the organic materials in bentonite.
** Assuming 0.1–100% corrosion of the iron.
TR-10-19
53
Table 2‑46. Estimated amounts of organic material from construction material classified as
foreign remaining after different periods in other areas in Laxemar.
Compound
Amounts left Left after
(kg)
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Concrete
additives
110
99
99
99
99
99
Asphalt:
bitumen
40
35
25
20
20
20
Acetate from
anaerobic steel
corrosion
23–2.3 × 104
0
0
0
0
0
Table 2‑47. Estimated amounts of carbohydrate material remaining after different periods in other
areas in Laxemar.
Compound
Urea
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
2
0
0
0
0
0
20
0
0
0
0
0
Organic materials
from ventilation
1
0
0
0
0
0
Wooden chips and
sawdust
10
7.5
5.0
5.0
5.0
5.0
Other human
waste
Table 2‑48. Estimated amounts of hydrocarbon material remaining after different periods in other
areas in Laxemar.
Compound
Amounts left
(kg)
Left after
100 years
(kg)
Left after
1,000 years
(kg)
Left after
10,000 years
(kg)
Left after
120,000 years
(kg)
Left
(kg)
Plastics
80
80
80
40
40
Rubber
*
*
*
*
*
*
110
55
0
0
0
0
Hydraulic and
lubrication oil
40
Hydrocarbon degradation will generally be somewhat slower than carbohydrate degradation. In
addition, in the case of hydrocarbons, the more easily degraded compounds will be degraded over
the first 100–10,000 years; the rest will remain after 120,000 years.
The organic material in both sites is presented in Table 2‑49. Here it can be seen that most of the
organic material is found in the bentonite, and it is questionable whether this material is available
for degradation. If this material is omitted, most of the organic material will be the acetate produced
using the energy in hydrogen from the anaerobic corrosion of steel. This is probably a much more
important source of organic material that can be degraded by microorganisms.
Table 2‑50 presents the theoretical amounts of hydrogen sulphide produced from acetate originating from the hydrogen produced by anaerobic iron corrosion in a repository; values from 100%
corrosion and 0.1% corrosion are presented. These values are used in Table 2‑51, together with the
calculated volumes of water in the different parts of the repository, presented in section 2.5.3.
In Forsmark, the highest calculated hydrogen sulphide concentration is 0.13 mg L–1 in the deposition
tunnels, while in Laxemar the highest value is 0.22 mg L–1. In the other areas, the highest values are
0.054 mg L–1 in Forsmark and 0.063 mg L–1 in Laxemar.
54
TR-10-19
Another source of organic material accessible to sulphate-reducing bacteria is the material in biofilms
on tunnel walls and ceilings. Using the values from sections 2.4 and 2.5.3, the theoretical concentrations of hydrogen sulphide produced from this material are calculated and presented in Table 2‑51.
These calculations presuppose no cleaning whatsoever of the rock walls before repository closure.
These theoretic calculation show that in Forsmark the highest calculated hydrogen sulphide concentration in the deposition tunnels from the degradation of microbial biofilms on rock surfaces is
5.8 × 10–3 g/L, the same value as found for the deposition tunnels of Laxemar. It has to be considered
that all numbers are uncertain.
The highest calculated hydrogen sulphide concentration found in the other areas of the repository is
2.3 × 10–3 g/L for both Forsmark and Laxemar.
Table 2‑49. Total amount of organic material in a repository, with and without the organic
materials in bentonite.
Deposition holes
Deposition tunnels
Other areas
With bentonite
organic
materials (kg)
Without ben‑
tonite organic
materials (kg)
With bentonite
organic
materials (kg)
Without ben‑
tonite organic
materials (kg)
With bentonite
organic
materials (kg)
Without ben‑
tonite organic
materials (kg)
Forsmark
9.8 × 105
–
5.1 × 106
1.3 × 104
8.5 × 106
1.8 × 104
Laxemar
9.8 × 105
–
1.9 × 107
2.0 × 104
1.2 × 107
2.3 × 104
Table 2‑50. Theoretical amounts of hydrogen sulphide produced from hydrogen originating from
anaerobic iron corrosion.
Deposition tunnels
Other areas
H2S from 100% iron
corrosion (mol)
H2S from 0.1% iron
corrosion (mol)
H2S from 100% iron
corrosion (mol)
H2S from 0.1% iron
corrosion (mol)
Forsmark
1.6 × 106
1.6 × 103
6.5 × 105
0.65 × 103
Laxemar
4.3 × 106
4.3 × 103
9.0 × 105
0.9 × 103
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55
56
Table 2-51. Theoretical concentrations of hydrogen sulphide produced from hydrogen originating from anaerobic iron corrosion in the different parts
of the repositories.
Deposition tunnels
Other areas
Concentration of
H2S: 100% iron
corrosion (g L–1)
Concentration of
H2S: 100% iron
corrosion (M)
Concentration of
H2S: 0.1% iron
corrosion (g L–1)
Concentration of
H2S: 0.1% iron
corrosion (M)
Concentration of
H2S: 100% iron
corrosion (g L–1)
Concentration of
H2S: 100% iron
corrosion (M)
Concentration of
H2S: 0.1% iron
corrosion (g L–1)
Concentration of
H2S: 0.1% iron
corrosion (M)
Forsmark
0.14
4 × 10–3
1.4 × 10–4
4 × 10–6
6.7 × 10–2
2.0 × 10–3
6.7 × 10–5
2.0 × 10–6
Laxemar
0.27
8 × 10
2.7 × 10
8 × 10
7.5 × 10
2.2 × 10
7.5 × 10
2.2 × 10–6
–3
–4
–6
–2
–3
–5
Table 2-52. Theoretical hydrogen sulphide concentrations produced by biofilms on rock surfaces in different areas of the repositories.
Deposition tunnels
Low density
Concentration
Concentration
(M)
(g/L)
High density
Concentration
(M)
Concentration
(g/L)
Other areas
Low density
Concentration
(M)
Concentration
(g/L)
High density
Concentration
(M)
Concentration
(g/L)
Forsmark
2.3 × 10–5
7.8 × 10–4
Laxemar
2.3 × 10–5
7.8 × 10–4
1.7 × 10–4
5.8 x10–3
9.0 × 10–6
3.1 × 10–4
6.8 × 10–5
2.3 × 10–3
1.7 × 10–4
5.8 × 10–3
9.0 × 10–6
3.0 × 10–4
6.7 × 10–5
2.3 × 10–3
TR-10-19
3
Summary and conclusions
The largest pool of organic material in a repository at closure is the organic material in the bentonite
in buffer and backfill. It is impossible to make any assumptions as to how much of this material
will be available for biodegradation, since the character of the material is unknown. However, it is
unlikely that this organic material can dissolve in groundwater unless the bentonite loses its swelling
capacity. The second largest pool will be the biofilms formed on the rock surfaces. This assumption
presupposes that no cleaning is undertaken before repository closure. The third largest pool is the
organic material produced by microorganisms using hydrogen from the anaerobic corrosion of iron
in steel as an energy source.
The following provides summary descriptions of the different pools of organic material that will
remain in the repository:
1. Microorganisms. Their effect would mainly be to reduce the redox potential soon after repository closure. They may contribute to the depletion of the oxygen entrapped during repository
construction, an effect that would not jeopardise repository stability.
If the dominant microorganisms in the anaerobic environment are sulphate-reducing bacteria,
oxidation of organic material would lead to the formation of HS−. The produced sulphide could
corrode the copper canisters under anaerobic conditions if it reaches them.
Another effect of microorganisms would be to increase the complexing capacity of the groundwater due to excreted metabolites. The impact of these compounds is not yet clear, although it
will surely not be very important, due to the small amounts of such substances.
2. Materials in the ventilation air. Their effect will probably be to help maintain reducing conditions in the area, although this effect will likely be minimal or negligible.
3. Construction materials. Among these materials, we emphasise the organic materials present in
concrete, asphalt, bentonite, and wood. Hydrocarbons from asphalt may help reduce the redox
potential within the repository. The products of cellulose degradation may help enhance the
complexing capacity of the groundwater around the repository, so the amount of cellulose left in
the repository should be minimised.
4. Fuels and engine emissions. No important effects are expected from these organic materials in the
repository. Although the presence of aromatic compounds and PAHs in groundwater is not desirable
in itself, these compounds are of no consequence for long-term repository performance.
5. Detergents and lubricants. The same reasoning as for fuels and engine emissions can be applied
to these materials. The amount of detergents should be minimised, although in the amounts in
which they are expected to occur, no important impact is foreseen.
6. Materials from human activities. Of these materials, fibres from clothes could have a more
important effect, due to the presence of cellulose. Accordingly, human-related wastes should me
minimised, although no large amounts of these materials are expected to be present after repository closure.
Three processes are considered to have the largest potential impact on repository performance:
i) Increasing the reducing capacity and reducing the redox potential in the short term, and increasing the depletion rate of oxygen trapped during the repository operation stage.
ii) Increasing the complexing capacity of the groundwater due to the presence of organic complexants, which is expected to be a more relevant process in the long term. Many organic molecules
with complexing capacity, for example, short-chain organic acids such as acetate, however, will
be oxidised due to microbial metabolism. The projected acetate concentration in groundwater
is below the detection limit of available analytical methods. The amount of organic material
in groundwater is usually only being a few mg L−1, and 25–75% of this material is non-humic
material, i.e. short-chain acids (see, e.g. /Nissinen et al. 2001/).
TR-10-19
57
iii)Production of HS− from the oxidation of short-chain organic acids by sulphate-reducing bacteria
using sulphate as an electron acceptor. The produced sulphide can corrode copper canisters if it
comes into contact with them.
The decrease in O2 concentration is a largely positive, so no specific measures need be taken to
counteract substances having only this effect contribution to safety. However, when oxygen is
depleted, sulphate reduction or some other anaerobic degradation process can occur. The increase in
complexing capacity, however, may be relevant if the organic matter degradation products coexist
with radionuclides over the long term or if they can exert an influence by worsening the performance
of the engineering barriers.
58
TR-10-19
TR-10-19
Table 3‑1. Organic material in a spent fuel repository: categories, chemical composition, possible effects, and recommended actions.
Categories of organic material
Chemical composition
Effect in the repository after closure
Recommended action
Growth of microorganisms
Biological compounds, EPSs, polymers, and
excreted metabolites.
Oxygen consuming, Eh lowering because of action as substrate for
groundwater microorganisms.
Possible increase in the complexation capacity due to the excreted
metabolites.
None
Study the amount of excreted metabolites.
Is it enough to provide important complexing capacity?
Organic material in
ventilation air
Biological compounds in seeds, spores, and
pollen.
Oxygen consuming, Eh lowering because of action as substrate for Minimise. Not foreseen to be important,
groundwater microorganisms.
due to the small amount of compounds
introduced in this way.
Construction materials
Concrete
Lignosulphonates, lignosulphates, sulphonated
Strongly bound to concrete particles. Possible decomposition in
naphthalene sulphonated formaldehyde, acryl sul- radiation field /Gascoyne 2002/ Probably no effect on the reposiphonate, alkyl sulphonate, and phenol ethoxylates. tory.
None
Asphalt
Heavy hydrocarbons and compounds containing
oxygen, sulphur, and nitrogen atoms
Some leakage to groundwater of low-molecular-weight hydrocarbons, some of which are biodegradable and thus Eh lowering.
Remove
Bentonite clay
Thought to be humic and fulvic acids as well as
humin, but not examined.
Function as substrate for microorganisms. Eh lowering but can
increase hydrogen sulphide production in the bentonite buffer.
Possible effect on Cu canisters.
None
Wood
Cellulose, lignin, and secondary products such as
tannins and terpenes.
Cellulose is both easily degraded by many microorganisms and
Remove
theoretically assumed to degrade under alkaline conditions, commonly projected to occurring in nuclear repositories that include
cement construction. Lignin is degraded by white rot fungi. Tannins
and terpenes are very slowly decomposed and can act as complex
binding agents. In summary, these species enhance the complexing capacity of the media.
Diesel
n-alkanes, PAHs, alkyl benzenes, aromatics,
branched and unsaturated aliphatic hydrocarbons,
and cycloaliphatic naphthenes.
Diesel hydrocarbons are easily degraded in the presence of oxygen, although condensed polyaromatic hydrocarbons (PAHs) are
slowly degraded. Degradation also occurs in anaerobic conditions.
Oxygen consumption and Eh lowering effects.
Engine emissions
Carbon soot, water, sulphuric acid, and condensed Condensed hydrocarbons can be degraded in the presence of
hydrocarbons.
oxygen but also by some anaerobic microorganisms.
Minimise
Rubber from tyres
Isoprene cross-linked with sulphur bridges.
Not easily degraded. Probably no effect on the repository.
Minimise
Detergents and Lubricants
Alkylbenzene sulphonates, alkylphenol
ethoxylates, plant-based tensides, and C18–C40
alkanes.
The “old” tensides are often difficult to degrade but “new” plantbased ones are more readily degraded. Oxygen depletion.
Minimise and if possible remove.
Fuels and engine emission
Minimise and if possible pump out.
59
60
Categories of organic material
Chemical composition
Effect in the repository after closure
Recommended action
Plant leaf components containing nicotine,
nornicotine, anabasine, myosmine, nicotyrine, and
anatabine.
Increase in the nitrate content of groundwater.
Minimise
Organic material from
human activities
Tobacco products
Cigarettes
Prohibit
Snuff
Including glycerol, sodium chloride, and sodium
carbonate.
Biodegradable. The amount can be easily minimised by restriction. Minimise
Dust from skin and hair
Protein
Biodegradable. No large effect expected.
None. Unavoidable.
Fibres from clothes
Polyesters
Cellulose
Polyesters will remain but probably not affect the repository. Cellulose is both biodegradable and easily degrades under alkaline
conditions common in nuclear waste repositories that include
cement construction. Not expected to be very important.
Remove
Urine
Urea, creatinine, ammonia, uric acid, and amino
acids.
Urine is degradable and functions as a nitrogen source for the
oxygen-consuming and Eh-lowering degradation in the repository.
Its degradation and consequent urea hydrolysis can increase the
pH. Should be minimised mainly for hygienic reasons. Expected
effect not very important.
Minimise
Paper and plastic waste
Cellulose and plastic polymers (see “Blasting”
below).
Cellulose will be biodegraded. Some plastics will be degraded and
others not depending on their composition. Can be avoided by
restriction.
Remove
Paper
Cellulose
Biodegradable. Large quantities can be removed. Small residues
can be left.
Remove
Plastics
Polyethylene terephthalate, polyethylene, polyvinylchloride, polypropylene, and polystyrene.
Most of these plastics are not biodegradable. There are so-called
bio-plastics produced by microorganisms and these are more or
less biodegradable.
Remove
Blasting and/or rock-drilling
TR-10-19
4
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